Lonh Vannsith, a fourth-year student of the National Polytechnic Institute of Cambodia, flies his team?s drone in Phnom Penh, Cambodia, September 17, 2021. Picture taken September 17, 2021. REUTERS/Cindy Liu

Students of the National Polytechnic Institute of Cambodia prepare their manned drone for flight, in Phnom Penh, Cambodia, September 17, 2021. Picture taken September 17, 2021. REUTERS/Cindy Liu

Lonh Vannsith, a fourth-year student of the National Polytechnic Institute of Cambodia, flies his team’s drone in Phnom Penh, Cambodia, September 17, 2021. Picture taken September 17, 2021. REUTERS/Cindy Liu

Lonh Vannsith, a fourth-year student of the National Polytechnic Institute of Cambodia, flies his team’s drone in Phnom Penh, Cambodia, September 17, 2021. Picture taken September 17, 2021. REUTERS/Cindy Liu

Students of the National Polytechnic Institute of Cambodia prepare their manned drone for flight, in Phnom Penh, Cambodia, September 17, 2021. Picture taken September 17, 2021. REUTERS/Cindy Liu

A drone built by students of the National Polytechnic Institute of Cambodia is seen in flight, in Phnom Penh, Cambodia, September 17, 2021. Picture taken September 17, 2021. REUTERS/Cindy Liu

Lonh Vannsith, a fourth-year student of the National Polytechnic Institute of Cambodia, and his teammates prepare their manned drone for flight in Phnom Penh, Cambodia, September 17, 2021. Picture taken September 17, 2021. REUTERS/Cindy Liu

Students of the National Polytechnic Institute of Cambodia prepare their manned drone for flight, in Phnom Penh, Cambodia, September 17, 2021. Picture taken September 17, 2021. REUTERS/Cindy Liu

Students of the National Polytechnic Institute of Cambodia prepare their manned drone for flight in Phnom Penh, Cambodia, September 17, 2021. Picture taken September 17, 2021. REUTERS/Cindy Liu

Ken Woo, 24, the acting president of the Hong Kong Polytechnic University student union, poses for a photograph outside a room for the student union on the campus in Hong Kong, China, May 10, 2021. "That period was traumatic for everyone in Hong Kong, physically or mentally," Woo said. "You think you didn't do well enough at that time or you blame yourself... If the world doesn’t change, the scars and pain will always be there." The university was the site of some of the most violent clashes between students and police in 2019. REUTERS/Lam Yik SEARCH "YIK SECURITY" FOR THIS STORY. SEARCH "WIDER IMAGE" FOR ALL STORIES

Plastic boards surround the outside area of the Hong Kong Polytechnic University in Hong Kong, China, April 27, 2021. The university was the site of some of the most violent clashes between students and police in 2019. REUTERS/Lam Yik SEARCH "YIK SECURITY" FOR THIS STORY. SEARCH "WIDER IMAGE" FOR ALL STORIES

Ana Maria Gonzalez wears a new innovation, a nasal mask designed by Mexican scientist Gustavo Acosta Altamirano, as a measure to protect against the coronavirus disease (COVID-19) transmission during the process of eating and drinking at the National Polytechnic Institute, in Mexico City, Mexico March 18, 2021. Picture taken March 18, 2021. REUTERS/Carlos Jasso

Ana Maria Gonzalez wears a new innovation, a nasal mask designed by Mexican scientist Gustavo Acosta Altamirano, as a measure to protect against the coronavirus disease (COVID-19) transmission during the process of eating and drinking at the National Polytechnic Institute, in Mexico City, Mexico March 18, 2021. Picture taken March 18, 2021. REUTERS/Carlos Jasso

Ana Maria Gonzalez wears a new innovation, a nasal mask designed by Mexican scientist Gustavo Acosta Altamirano, as a measure to protect against the coronavirus disease (COVID-19) transmission during the process of eating and drinking at the National Polytechnic Institute, in Mexico City, Mexico March 18, 2021. Picture taken March 18, 2021. REUTERS/Carlos Jasso

Mexican scientist Gustavo Acosta Altamirano shows his new innovation, a nasal mask as a measure to protect against the coronavirus disease (COVID-19) transmission during the process of eating and drinking at the National Polytechnic Institute, in Mexico City, Mexico March 18, 2021. Picture taken March 18, 2021. REUTERS/Carlos Jasso

Mexican scientist Gustavo Acosta Altamirano shows his new innovation, a nasal mask as a measure to protect against the coronavirus disease (COVID-19) transmission during the process of eating and drinking at the National Polytechnic Institute, in Mexico City, Mexico March 18, 2021. Picture taken March 18, 2021. REUTERS/Carlos Jasso TPX IMAGES OF THE DAY

A view of a manhole cover near the Kwun Yam Temple in Hong Kong's Hung Hom district, leading to a network of sewers connected to the Hong Kong Polytechnic University (PolyU) in Hong Kong, China, September 29, 2020. Hundreds of protesters trapped during the siege of PolyU last November used this network of sewers to escape, which volunteers like Dave, a diver, helped scout out. Picture taken September 29, 2020. REUTERS/James Pomfret To match Special Report HONGKONG-DEMOCRACY/ACTIVISTS

A view of Hong Kong Polytechnic University (PolyU) and the Cross Harbour Tunnel next to it in Hong Kong, China, October 1, 2020. Picture taken October 1, 2020. REUTERS/James Pomfret To match Special Report HONGKONG-DEMOCRACY/ACTIVISTS

Dave, a diver, holds a reel of diving thread, similar to what he used during the November 2019 siege of the Hong Kong Polytechnic University (PolyU) when he dived into the submerged sewage system from Victoria Harbour to help scout a subterranean escape route from the campus, as he participates in a recent diving expedition in the waters off Hong Kong, China, in this undated image. REUTERS/Staff To match Special Report HONGKONG-DEMOCRACY/ACTIVISTS

Dave, a diver, participates in a recent diving expedition in the waters off Hong Kong, China, in this undated image. During the November 2019 siege of the Hong Kong Polytechnic University (PolyU), Dave dived into the submerged sewage system from Hong Kong’s iconic Victoria Harbour, helping to scout a subterranean escape route from the campus. REUTERS/Staff To match Special Report HONGKONG-DEMOCRACY/ACTIVISTS

Dave, a diver, participates in a recent diving expedition in the waters off Hong Kong, China, in this undated image. During the November 2019 siege of the Hong Kong Polytechnic University (PolyU), Dave dived into the submerged sewage system from Hong Kong's iconic Victoria Harbour, helping to scout a subterranean escape route from the campus. REUTERS/Staff To match Special Report HONGKONG-DEMOCRACY/ACTIVISTS

A police officer wearing a protective face mask walks past the closed entrance of the Athens' Polytechnic School, as the Greek government banned the annual march marking the anniversary of a 1973 student revolt against the then military junta due to the coronavirus disease (COVID-19) pandemic, in Athens, Greece, November 17, 2020. REUTERS/Alkis Konstantinidis

A wreath is placed on the closed entrance of the Athens' Polytechnic School, as the Greek government banned the annual march marking the anniversary of a 1973 student revolt against the then military junta due to the coronavirus disease (COVID-19) pandemic, in Athens, Greece, November 17, 2020. REUTERS/Alkis Konstantinidis

Hong Kong's Commissioner of Police Chris Ping-keung Tang walks outside Hong Kong Polytechnic University (PolyU) in Hong Kong, China November 19, 2019. Picture taken November 19, 2019. REUTERS/Adnan Abidi To match Special Report HONGKONG-PROTESTS/SECURITY-POLICE

A health worker holds a box with a sign reading "Transport of samples COVID-19" at the National Polytechnic Institute (IPN) where test are being taken, as the coronavirus disease (COVID-19) outbreak continues, in Mexico City, Mexico June 17, 2020. REUTERS/Henry Romero

A member of biological sciences of the National Polytechnic Institute (IPN) tests a woman for the coronavirus disease (COVID-19) at the university, as the coronavirus disease (COVID-19) outbreak continues, in Mexico City, Mexico June 17, 2020. REUTERS/Henry Romero

Members of biological sciences of the National Polytechnic Institute (IPN) test people for the coronavirus disease (COVID-19) at the university, as the coronavirus disease (COVID-19) outbreak continues, in Mexico City, Mexico June 17, 2020. REUTERS/Henry Romero

A member of biological sciences of the National Polytechnic Institute (IPN) tests a woman for the coronavirus disease (COVID-19) at the university, as the coronavirus disease (COVID-19) outbreak continues, in Mexico City, Mexico June 17, 2020. REUTERS/Henry Romero

Members of biological sciences of the National Polytechnic Institute (IPN) test people for the coronavirus disease (COVID-19) at the university, as the coronavirus disease (COVID-19) outbreak continues, in Mexico City, Mexico June 17, 2020. REUTERS/Henry Romero

A member of biological sciences of the National Polytechnic Institute (IPN) tests a woman for the coronavirus disease (COVID-19) at the university, as the coronavirus disease (COVID-19) outbreak continues, in Mexico City, Mexico June 17, 2020. REUTERS/Henry Romero

A doctor shows the drug Oral Transferon, which is part of a protocol at the National Polytechnic Institute (IPN) to evaluate the effects of its treatment in patients with the coronavirus disease (COVID-19), as the outbreak of the COVID-19 continues, in Mexico City, Mexico May 19, 2020. REUTERS/Carlos Jasso

A woman signs herself into a clinical protocol to be treated with the drug Oral Transferon, which aims to evaluate the effects of its treatment in patients with the coronavirus disease (COVID-19), at the National Polytechnic Institute (IPN), as the outbreak of the COVID-19 continues, in Mexico City, Mexico May 19, 2020. REUTERS/Carlos Jasso

A member of biological sciences of the National Polytechnic Institute (IPN) tests a woman for the coronavirus disease (COVID-19) at the university, as the outbreak of the COVID-19 continues, in Mexico City, Mexico May 19, 2020. REUTERS/Carlos Jasso

Members of biological sciences of the National Polytechnic Institute (IPN) test men for the coronavirus disease (COVID-19) at the university, as the outbreak of the COVID-19 continues, in Mexico City, Mexico May 19, 2020. REUTERS/Carlos Jasso TPX IMAGES OF THE DAY

A member of biological sciences of the National Polytechnic Institute (IPN) tests a man for the coronavirus disease (COVID-19) at the university, as the outbreak of the COVID-19 continues, in Mexico City, Mexico May 19, 2020. REUTERS/Carlos Jasso

A member of biological sciences of the National Polytechnic Institute (IPN) tests a man for the coronavirus disease (COVID-19) at the university, as the outbreak of the COVID-19 continues, in Mexico City, Mexico May 19, 2020. REUTERS/Carlos Jasso

Members of biological sciences of the National Polytechnic Institute (IPN) test men for the coronavirus disease (COVID-19) at the university, as the outbreak of the COVID-19 continues, in Mexico City, Mexico May 19, 2020. REUTERS/Carlos Jasso

A member of biological sciences of the National Polytechnic Institute (IPN) tests a man for the coronavirus disease (COVID-19) at the university, as the outbreak of the COVID-19 continues, in Mexico City, Mexico May 19, 2020. REUTERS/Carlos Jasso

A member of biological sciences of the National Polytechnic Institute (IPN) rests before testing patients for the coronavirus disease (COVID-19) at the university, as the outbreak of the COVID-19 continues, in Mexico City, Mexico May 19, 2020. REUTERS/Carlos Jasso

A member of biological sciences of the National Polytechnic Institute (IPN) tests a man for the coronavirus disease (COVID-19) at the university, as the outbreak of the COVID-19 continues, in Mexico City, Mexico May 19, 2020. REUTERS/Carlos Jasso

A man clears debris following the clashes between police and anti-government protester after a two week campus siege of the Polytechnic University in Hong Kong, China, November 16, 2019. Reuters has been awarded the 2020 Pulitzer Prize in Breaking News Photography for Hong Kong protests. REUTERS/Adnan Abidi TPX IMAGES OF THE DAY

A prototype of a ventilator is seen at a polytechnic laboratory amid an outbreak of the coronavirus disease (COVID-19), in Thies, Senegal April 7, 2020. Picture taken April 7,2020. REUTERS/Zohra Bensemra

Scientist Dr Ibrahima Gueye talks to a journalist as he stands beside a prototype of a ventilator he developed with a team, at a polytechnic laboratory, amid an outbreak of the coronavirus disease (COVID-19), in Thies, Senegal April 7, 2020. Picture taken April 7,2020. REUTERS/Zohra Bensemra

Scientist Dr Ibrahima Gueye talks to a journalist as he stands beside a prototype of a ventilator he developed with a team, at a polytechnic laboratory, amid an outbreak of the coronavirus disease (COVID-19), in Thies, Senegal April 7, 2020. Picture taken April 7,2020. REUTERS/Zohra Bensemra

Cherry blossoms bloom at the University of Washington, which has suspended in-person classes, during the outbreak of coronavirus disease (COVID-19), in Seattle, Washington, U.S., March 16, 2020. Picture taken March 16, 2020. REUTERS/Lindsey Wasson

Two frontline lovers in full body gear hug each other in the besieged Hong Kong Polytechnic University (PolyU) campus that had been on lockdown for a week in Hong Kong, China on November 18, 2019. Picture taken November 18, 2019. REUTERS/Jessie Pang

Graffiti with Chinese words “Why have universities become battlegrounds?” is seen at he Hong Kong Polytechnic University (PolyU) campus that has been on lockdown for a week in Hong Kong, China November 23, 2019. Picture taken November 23, 2019. REUTERS/Jessie Pang

A rainbow forms near the bridge where protesters made a daring escape past walls of riot police at the Hong Kong Polytechnic University (PolyU) campus that has been on lockdown for a week in Hong Kong, China November 19, 2019. Picture taken November 19, 2019. REUTERS/Jessie Pang

A decorated statue is seen in a building inside of a nearly empty Hong Kong Polytechnic University (PolyU) as the campus continues to be closed by police in Hong Kong, China, November 27, 2019. Picture taken November 27, 2019. REUTERS/Leah Millis

An abandoned shoe lays on a graffitied ground inside of a nearly empty Hong Kong Polytechnic University (PolyU) as the campus continues to be closed by police in Hong Kong, China, November 27, 2019. Picture taken November 27, 2019. REUTERS/Leah Millis

A classroom that was converted into a living space by desperate protesters, trapped inside of Hong Kong Polytechnic University (PolyU) can be seen on the campus under siege by the police in Hong Kong, China, November 22, 2019. Picture taken November 22, 2019. REUTERS/Leah Millis

A sign and graffiti are seen inside of Hong Kong Polytechnic University (PolyU) as the campus continues to be closed by police in Hong Kong, China, November 27, 2019. Picture taken November 27, 2019. REUTERS/Leah Millis

People walk through a courtyard inside of Hong Kong Polytechnic University (PolyU) as the campus continues to be closed by police in Hong Kong, China, November 27, 2019. Picture taken November 27, 2019. REUTERS/Leah Millis

A wrecked umbrella, gloves, arrows and other items are seen covered in leaves and dried blue substance from a police water cannon inside of the Hong Kong Polytechnic University (PolyU), the campus under siege by police in Hong Kong, China, November 27, 2019. Picture taken November 27, 2019. REUTERS/Leah Millis

Trampled protest signs can be seen on the ground inside of Hong Kong Polytechnic University (PolyU) as the campus continues to be closed by police in Hong Kong, China, November 27, 2019. Picture taken November 27, 2019. REUTERS/Leah Millis

An abandoned umbrella and a bow lay on the ground inside of Hong Kong Polytechnic University (PolyU) as the campus continues to be closed by police in Hong Kong, China, November 27, 2019. Picture taken November 27, 2019. REUTERS/Leah Millis

A glove lays abandoned on graffitied ground inside of Hong Kong Polytechnic University (PolyU) as the campus continues to be closed by police in Hong Kong, China, November 27, 2019. Picture taken November 27, 2019. REUTERS/Leah Millis

Workers can be seen repairing the sidewalk outside of Hong Kong Polytechnic University (PolyU) as the campus continues to be closed by police in Hong Kong, China, November 27, 2019. Picture taken November 27, 2019. REUTERS/Leah Millis

Charred papers lay on the ground inside of Hong Kong Polytechnic University (PolyU) as the campus continues to be closed by police in Hong Kong, China, November 27, 2019. Picture taken November 27, 2019. REUTERS/Leah Millis

Zip-ties, old crackers, medical supplies, a fire blanket and a power drill are among items that lay abandoned on a table inside of Hong Kong Polytechnic University (PolyU) as the campus continues to be closed by police in Hong Kong, China, November 27, 2019. Picture taken November 27, 2019. REUTERS/Leah Millis