Paramedic Christian Boyd, one of the first responders on 9/11, rings a bell of remembrance for each person who died on the hijacked United Airlines Flight 93 plane crash, during an event commemorating the 20th anniversary of the September 11, 2001 attacks at the Flight 93 National Memorial in Stoystown, Pennsylvania, U.S., September 11, 2021. REUTERS/Evelyn Hockstein