An NHS worker explains the coronavirus disease (COVID-19) testing protocol to local residents at a mobile testing unit in Tower Hamlets, London, Britain, May 2, 2021. REUTERS/Peter Nicholls

An NHS worker explains the coronavirus disease (COVID-19) testing protocol to local residents at a mobile testing unit in Tower Hamlets, London, Britain, May 2, 2021. REUTERS/Peter Nicholls

Churchill Downs' workers hand flyers, explaining their strike, to spectators that come to watch the 147th Oaks race, a day before Kentucky Derby in Louisville, Kentucky, U.S. April 30, 2021. REUTERS/Amira Karaoud

Michele Benincaso, founder of Elk, explains how the Aloha device reduces audio latency, Stockholm, Sweden, April 14, 2021. Picture taken April 14, 2021 REUTERS/Supantha Mukherjee

Naelyn Pike plays with dogs in San Carlos, Arizona, U.S., March 31, 2021. "I remember as a young girl, at six years old, seeing my grandfather wearing a bulletproof vest trying to explain to the townspeople of Superior how important the protection of our land is against Resolution Copper," said Pike. Pike's grandfather Dr. Wendsler Nosie, Sr. has been living at Oak Flat for the last year and a half praying for the land and drawing attention to Apache Stronghold's fight to save the sacred land. "I think a lot of people get a misconception that the Oak Flat movement just began like within the last year or so, but my grandfather's been fighting this fight for over 18 years." Picture taken March 31, 2021. REUTERS/Caitlin O'Hara

The Oak Flat campground in the Tonto National Forest, Arizona, U.S., March 31, 2021. "I remember as a young girl, at six years old, seeing my grandfather wearing a bulletproof vest trying to explain to the townspeople of Superior how important the protection of our land is against Resolution Copper," said Naelyn Pike. Pike's grandfather Dr. Wendsler Nosie Sr. has lived at Oak Flat campground for the past year and a half. Picture taken March 31, 2021. REUTERS/Caitlin O'Hara

Jen Mondillo, a volunteer vaccine administrator, explains the procedures at a coronavirus disease (COVID-19) vaccine clinic run by Skippack Pharmacy in Lansdale, Pennsylvania, U.S., April 18, 2021.

A health worker explains the vaccination process to people as the coronavirus disease (COVID-19) outbreak continues, at the Tecnopolis Park, in Buenos Aires, Argentina April 15, 2021. REUTERS/Agustin Marcarian

Nurse Will Grima reaches Rebecca Zammit Lupi's Hickman line to administer medication through it as she sleeps in her room in Rainbow Ward at Sir Anthony Mamo Oncology Centre in Mater Dei Hospital, during the coronavirus disease (COVID-19) outbreak, in Tal-Qroqq, Malta October 8, 2020. Grima said, "Working with teens, children and babies, you get to see them overcome tribulations and watch as they grow from them. Sadly, sometimes the challenge is too great. In those times, we try to make whatever time they have as meaningful as possible. I can remember the excitement on Rebecca's face when she would show me one of the games she had been playing with Darrin: Sky. She'd explain the mechanics of the game to me, show me some outfits she'd received for her character and so on. You could see from the way her face lit up that she was enjoying it, so when I had some free time I'd try to steal a few minutes and watch Rebecca play. She'd either be showing her father the ropes as they played together, or blasting through levels with pinpoint accuracy from all the practice. Memories like these are bittersweet; I can't help but feel sad about what Rebecca and her parents had to endure, yet it's moments like those that make our line of work meaningful." REUTERS/Darrin Zammit Lupi SEARCH "REBECCA LUPI" FOR THIS STORY. SEARCH "WIDER IMAGE" FOR ALL STORIES THE IMAGES SHOULD ONLY BE USED TOGETHER WITH THE STORY - NO STAND-ALONE USES TPX IMAGES OF THE DAY

Radiographer Maria Elena Grech explains how radiotherapy works to Rebecca Zammit Lupi, a 14-year-old cancer patient, while showing her images, at Sir Anthony Mamo Oncology Centre in Mater Dei Hospital, during the coronavirus disease (COVID-19) outbreak, in Tal-Qroqq, Malta, May 15, 2020. Rebecca had been considering radiotherapy as a possible career choice. Grech said "Even though her radiotherapy treatment wasn't a pleasant experience for her, Becs was eager to learn and ask questions - and we enjoyed explaining to her. She never gave up on learning which was very inspiring for us all." REUTERS/Darrin Zammit Lupi SEARCH "REBECCA LUPI" FOR THIS STORY. SEARCH "WIDER IMAGE" FOR ALL STORIES THE IMAGES SHOULD ONLY BE USED TOGETHER WITH THE STORY - NO STAND-ALONE USES

Long COVID sufferer Susana Matarranz, a 44-year-old primary school teacher, poses for a photograph taken through blue plastic, in Madrid, Spain, March 8, 2021. The photograph was taken through blue plastic to visualise the effects of long COVID. Matarranz gets emotional when she explains how much she misses her students. Matarranz got infected on March 1, 2020. At first, she only noticed the loss of smell and taste, but soon afterwards she started suffering from severe stomach problems and acute joint pain. "My right collar bone is swollen, I can barely lift my arm, I feel like I have aged prematurely," she said. Matarranz returned to work in September, but got infected a second time in November and hasn't been able to continue teaching ever since. "The part of me that is my profession is empty, like that blackboard. A piece of my heart, which are my students, whom I love dearly, feels empty and I feel like at this moment there's nothing I can do to fill it in." REUTERS/Susana Vera SEARCH "SPAIN LONGCOVID" FOR THIS STORY. SEARCH "WIDER IMAGE" FOR ALL STORIES. TPX IMAGES OF THE DAY.

A blank children's blackboard is photographed through blue plastic at the home of long COVID sufferer Susana Matarranz, a 44-year-old primary school teacher, in Madrid, Spain, March 8, 2021. The photograph was taken through blue plastic to visualise the effects of long COVID. Matarranz gets emotional when she explains how much she misses her students. Matarranz got infected on March 1, 2020. At first, she only noticed the loss of smell and taste, but soon afterwards she started suffering from severe stomach problems and acute joint pain. "My right collar bone is swollen, I can barely lift my arm, I feel like I have aged prematurely," she said. Matarranz returned to work in September, but got infected a second time in November and hasn't been able to continue teaching ever since. "The part of me that is my profession is empty, like that blackboard. A piece of my heart, which are my students, whom I love dearly, feels empty and I feel like at this moment there's nothing I can do to fill it in." REUTERS/Susana Vera SEARCH "SPAIN LONGCOVID" FOR THIS STORY. SEARCH "WIDER IMAGE" FOR ALL STORIES

A combination picture shows long COVID sufferer Susana Matarranz, a 44-year-old primary school teacher, posing for a photograph taken through blue plastic, and a blank blackboard photographed through blue plastic at Matarranz's home, in Madrid, Spain, March 8, 2021. The photographs were taken through blue plastic to visualise the effects of long COVID. Matarranz gets emotional when she explains how much she misses her students. Matarranz got infected on March 1, 2020. At first, she only noticed the loss of smell and taste, but soon afterwards she started suffering from severe stomach problems and acute joint pain. "My right collar bone is swollen, I can barely lift my arm, I feel like I have aged prematurely," she said. Matarranz returned to work in September, but got infected a second time in November and hasn't been able to continue teaching ever since. "The part of me that is my profession is empty, like that blackboard. A piece of my heart, which are my students, whom I love dearly, feels empty and I feel like at this moment there's nothing I can do to fill it in." REUTERS/Susana Vera SEARCH "SPAIN LONGCOVID" FOR THIS STORY. SEARCH "WIDER IMAGE" FOR ALL STORIES. TPX IMAGES OF THE DAY.

Nurse Guillermo Monzon explains to a relative of Carmen Vera the side effects after reciting Pfizer's COVID-19 vaccine, in Telde, on the island of Gran Canaria, Spain March 31, 2021. Picture taken March 31, 2021. REUTERS/Borja Suarez

Nurse Guillermo Monzon explains to a relative of Carmen Garcia the side effects after administering Pfizer's COVID-19 vaccine, in Telde, on the island of Gran Canaria, Spain March 31, 2021. Picture taken March 31, 2021. REUTERS/Borja Suarez

Nurse Guillermo Monzon explains to a relative of Juan Perez the side effects after administering Pfizer's COVID-19 vaccine, in Telde, on the island of Gran Canaria, Spain March 31, 2021. Picture taken March 31, 2021. REUTERS/Borja Suarez

Israeli Prime Minister Benjamin Netanyahu, wearing a face mask, looks as his corruption trial resumes, at Jerusalem's District Court April 5, 2021. Abir Sultan/Pool via REUTERS

Angela Harrelson, George Floyd's aunt, explains to a passerby the exhibits in the Chicago Avenue Fire Arts Center at George Floyd Square on the fifth day in the trial of former police officer Derek Chauvin, who is facing murder charges in the death of George Floyd, in Minneapolis, Minnesota, U.S., April 2, 2021. REUTERS/Nicholas Pfosi

A specialist trainer explains to women as they participate in efforts to clear landmines in Basra, Iraq March 27, 2021. Picture taken March 27, 2021. REUTERS/Mohammed Aty. NO RESALES. NO ARCHIVES.

Armin Laschet, head of Germany's Christian Democratic Union (CDU) party, wears a mask as he explains slogans after a news conference on the CDU programme for the general election, in Berlin, Germany March 30, 2021. Tobias Schwarz/Pool via REUTERS

Armin Laschet, head of Germany's Christian Democratic Union (CDU) party, wears a mask as he explains slogans after a news conference on the CDU programme for the general election, in Berlin, Germany March 30, 2021. Tobias Schwarz/Pool via REUTERS

A worker from a traffic controls unit explains how a camera that uses an experimental 5G network placed in Santiago works, in Santiago, Chile March 19, 2021. Picture taken March 19, 2021. REUTERS/Ivan Alvarado

A visual explainer about common and rare conditions linked to the coronavirus vaccines

A veterinarian explains the process of emigrating with his pets to dog owner Don Yip before their emigration to Britain, in Hong Kong, China February 15, 2021. Picture taken February 15, 2021.REUTERS/Tyrone Siu

Lord Mayor Boris Palmer (L) and the city?s pandemic medical advisor, Lisa Federle explain their strategy of testing and issuing day passes which allow people to visit shops and cultural institutions, as the spread of the coronavirus disease (COVID-19) continues in Tuebingen, Germany, March 17, 2021. REUTERS/Kai Pfaffenbach

Kazuyoshi Sasaki, 67, who lost his wife, Miwako, in the March 11, 2011 earthquake and tsunami, reacts as he calls his late wife inside Kazo-no-Denwa (the phone of the wind), a phone booth set up for people to call their deceased loved ones, ahead of the 10th anniversary of the disaster, at Bell Gardia Kujira-yama in Otsuchi town, Iwate Prefecture, northern Japan, February 27, 2021. Inside, Sasaki dials his wife's cellphone number. He explains how he searched for her for days. "It all happened in an instant, I can't forget it even now," he says, weeping. "I sent you a message telling you where I was, but you didn't check it. When I came back to the house and looked up at the sky, there were thousands of stars, it was like looking at a jewel box," he added. "I cried and cried and knew then that so many people must have died." REUTERS/Issei Kato SEARCH "KATO PHONEBOOTH" FOR THIS STORY. SEARCH "WIDER IMAGE" FOR ALL STORIES. TPX IMAGE OF THE DAY.

Kazuyoshi Sasaki, 67, who lost his wife, Miwako, in the March 11, 2011 earthquake and tsunami disaster, reacts as he steps out of Kazo-no-Denwa (The phone of the Wind), a phone booth set up for people to call their deceased loved ones, after calling his late wife, ahead of the 10th anniversary of when the disaster happened, at Bell Gardia Kujira-yama in Otsuchi town, Iwate Prefecture, northern Japan, February 27, 2021. "It all happened in an instant, I can't forget it even now," Sasaki said when he explained how he searched for her for days after the devastating earthquake and tsunami a decade ago, visiting evacuation centres and makeshift morgues, returning at night to the rubble of their home. "I sent you a message telling you where I was, but you didn't check it," he added. "When I came back to the house and looked up at the sky, there were thousands of stars, it was like looking at a jewel box," he said. "I cried and cried and knew then that so many people must have died." REUTERS/Issei Kato SEARCH "KATO PHONEBOOTH" FOR THIS STORY. SEARCH "WIDER IMAGE" FOR ALL STORIES

Peter van Wees explains John Moritz when to shout in the quick breath analyzer cabin that tests for the coronavirus disease (COVID-19) at a testing location in Amsterdam, Netherlands March 1, 2021. Picture taken March 1, 2021. REUTERS/Eva Plevier

Employee Semrad Ucak explains North Rhine-Westphalia (NRW) State Premier Armin Laschet how a COVID-19 quick antigen test works, during his visit of the production of "nal von minden" amid the outbreak of the coronavirus disease (COVID-19) in Moers, Germany, March 2, 2021. Federico Gambarini/Pool via REUTERS

Employee Semrad Ucak explains North Rhine-Westphalia (NRW) State Premier Armin Laschet how a COVID-19 quick antigen test works, during his visit of the production of "nal von minden" amid the outbreak of the coronavirus disease (COVID-19) in Moers, Germany, March 2, 2021. Federico Gambarini/Pool via REUTERS

Employee Semrad Ucak explains North Rhine-Westphalia (NRW) State Premier Armin Laschet how a COVID-19 quick antigen test works, during his visit of the production of "nal von minden" amid the outbreak of the coronavirus disease (COVID-19) in Moers, Germany, March 2, 2021. Federico Gambarini/Pool via REUTERS

CORRECTION This story were updated to make clear that bats are suspected to be the source of the novel coronavirus but not proven. As the World Health Organization reaches its findings on the zoonotic origins of the novel coronavirus, we explain why bats make such ideal hosts for disease-causing viruses.

A 21st century construction boom is driving unregulated sand mining around the world - eroding rivers and coastlines, disrupting ecosystems and hurting livelihoods.

A sign is posted at a Trader Joe's supermarket explaining its empty shelves on inclement weather, in Metairie, Louisiana, U.S. February 18, 2021. REUTERS/Scott Balling

An Indo-Tibetan Border Police (ITBP) officer explains the location of affected villages on a map at a temporary base camp set up by ITBP for distribution of relief material in the affected areas, after a flash flood swept a mountain valley destroying dams and bridges, at Lata village in Chamoli district, in the northern state of Uttarakhand, India, February 12, 2021. REUTERS/Anushree Fadnavis

Maria Elena Sandoval, 78, explains how she saved her foot from thrombosis thanks to private surgery paid for by the money from her son who works in the U.S., at her house in Jantetelco, state of Morelos, Mexico November 12, 2020. Picture taken November 12, 2020. REUTERS/Carlos Jasso

Maps and photos explaining what happened during the Republic Day tractor rally

Kyuta Kumagai, 10, practices sumo with his father Taisuke, 50, during a one-on-one training session which his father organized at the Buddhist temple Joshin-ji in Tokyo, Japan, September 2, 2020. "I think he is managing to make time for himself and I think he has time to play with his friends," explained Taisuke. "I don't think it is too much pressure." REUTERS/Kim Kyung-Hoon SEARCH "KYUNG-HOON SUMO" FOR THIS STORY. SEARCH "WIDER IMAGE" FOR ALL STORIES

A note explaining the temporary closure by authorities due to COVID-19 measures is placed on the door of the Muensterhoefli restaurant, as the spread of the coronavirus disease continues, in Zurich, Switzerland January 11, 2021. REUTERS/Arnd Wiegmann

A note explaining the temporary closure by authorities due to COVID-19 measures is placed on the door of the Confiserie Spruengli restaurant, as the spread of the coronavirus disease continues, in Zurich, Switzerland January 11, 2021. REUTERS/Arnd Wiegmann

College students Jester Rafon, 20, Rosemine Gonzaga, 19, Jenebyl Cipres, 19, and Almer Acuno, 21, hike up a mountain to find a spot where there is internet connection in order to take part in online classes, following the suspension of physical classes during the coronavirus disease (COVID-19) outbreak, in Sitio Papatahan, Paete, Laguna, Philippines, October 22, 2020. "I was really excited for college because all my life I've been here in the mountains," Gonzaga said, explaining how the pandemic had thwarted her plans for an independent life in the town. REUTERS/Eloisa Lopez SEARCH "LOPEZ SCHOOL ONLINE" FOR THIS STORY. SEARCH "WIDER IMAGE" FOR ALL STORIES

Respiratory therapist Annette James wears personal protective equipment as she explains how to use a mucus extractor to her patient Geraldine Sprys, who is suffering from pneumonia, at Medical Arts Hospital in Lamesa, Texas, U.S., December 17, 2020. Picture taken December 17, 2020. REUTERS/Go Nakamura

Dr. Eileen Sprys draws for her patient to explain about medications at Medical Arts Hospital in Lamesa, Texas, U.S., December 17, 2020. Picture taken December 17, 2020. REUTERS/Go Nakamura

Dr. Eileen Sprys explains about medicines to patient Stan Waldrop at Medical Arts Hospital in Lamesa, Texas, U.S., December 17, 2020. Picture taken December 17, 2020. REUTERS/Go Nakamura

Tate Trujillo, director of pharmacy, explains the cold storage units that will store the Pfizer coronavirus disease (COVID-19) vaccine at Indiana University Health in Indianapolis, Indiana, U.S., December 11, 2020. REUTERS/Bryan Woolston

Tate Trujillo, director of pharmacy, explains the cold storage units that will store the Pfizer coronavirus disease (COVID-19) vaccine at Indiana University Health in Indianapolis, Indiana, U.S., December 11, 2020. REUTERS/Bryan Woolston

Tate Trujillo, director of pharmacy, explains the cold storage units and shipping containers used for the Pfizer coronavirus disease (COVID-19) vaccine at Indiana University Health in Indianapolis, Indiana, U.S., December 11, 2020. REUTERS/Bryan Woolston

Tate Trujillo, director of pharmacy, explains shipping containers for the Pfizer coronavirus disease (COVID-19) vaccine at Indiana University Health in Indianapolis, Indiana, U.S., December 11, 2020. REUTERS/Bryan Woolston

UPDATE Updates with Mar. 3, 2021 explosion. Graphic explaining SpaceX's failed Starship test launch and explosion.

Diagram explaining Japan's Hayabusa2 mission.

A store worker explains coronavirus protocols to a shopper at the Citadel Outlet mall, as the global outbreak of the coronavirus disease (COVID-19) continues, in Commerce, California, U.S., December 3, 2020. REUTERS/Lucy Nicholson

Lesya Lytvynova, co-founder of the Kyiv-based charity fund "Ours", explains how to use an oxygen generator while speaking with a son of an elderly man, whose arterial blood oxygen saturation level dropped below 88 percent, in her office in Kyiv, Ukraine November 20, 2020. The charity fund gives free generators to patients suffering respiratory distress, plugging a shortage in Ukraine's healthcare system as the coronavirus disease (COVID-19) cases spike to record levels. Picture taken November 20, 2020. REUTERS/Gleb Garanich

Lesya Lytvynova, co-founder of the Kyiv-based charity fund "Ours", explains how to use an oxygen generator while speaking with Olga Sabatiye, whose mother Halyna Panasiuk tested positive for coronavirus, in her office in Kyiv, Ukraine November 20, 2020. The charity fund gives free generators to patients suffering respiratory distress, plugging a shortage in Ukraine's healthcare system as the coronavirus disease (COVID-19) cases spike to record levels. Picture taken November 20, 2020. REUTERS/Gleb Garanich

Artist Ahlam Nasser explains pieces she painted at her home yard in Sanaa, Yemen November 23, 2020. Picture taken November 23, 2020. REUTERS/Khaled Abdullah

French anaesthesiologist Caroline Tesse, 34, talks with her daughter Margaux during a session to explain her job to the schoolchildren at the primary school in Villeneuve d'Ascq after returning home from a four-day shift at the Intensive Care Unit (ICU) where patients suffering from the coronavirus disease (COVID-19) are treated at Cambrai hospital, France, November 17, 2020. Picture taken, November 17, 2020. REUTERS/Pascal Rossignol

A woman smiles as member of the community swabbing team explains the procedure before carrying out a doorstep COVID-19 test following the outbreak of the coronavirus disease (COVID-19) in Chadderton, Britain, September 30, 2020. Picture taken September 30, 2020. To match Special Report HEALTH-CORONAVIRUS/BRITAIN-NEWWAVE REUTERS/Phil Noble

A statement, which explains the closure, is placed at the entrance of the Swissotel hotel, as the spread of the coronavirus disease (COVID-19) continues, in Zurich, Switzerland November 17, 2020. REUTERS/Arnd Wiegmann

A statement from gastronomy group Holenstein Gastro which explains the temporary closure of Bierhalle Wolf beer hall to bridge the low demand during the COVID-19 period, as the spread of the coronavirus disease (COVID-19) continues, is seen in Zurich, Switzerland November 4, 2020. REUTERS/Arnd Wiegmann

Riot police stand guard as protesters take part in a rally outside the Constitutional Court building, demanding the judges come out and explain to them the reasons for their ruling on the anti-graft laws in Kyiv, Ukraine October 30, 2020. REUTERS/Gleb Garanich

A protester throws a smoke bomb during a rally outside the Constitutional Court building, demanding the judges come out and explain to them the reasons for their ruling on the anti-graft laws in Kyiv, Ukraine October 30, 2020. REUTERS/Gleb Garanich