People join U.S. Vice President Kamala Harris (3d L) as she walks towards the boulder which marks the general location of the impact site where the hijacked United Airlines Flight 93 plane crashed 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