Lanterns are placed at the Wall of Names during a candlelight memorial to the passengers and crew of United Airlines Flight 93 in Shanksville, Pennsylvania, the United States, Sept. 10, 2021. Memorials were held at the Flight 93 National Memorial in Pennsylvania to mark the 20th anniversary of the Sept. 11 attacks.(Photo: Xinhua)

People visit the Wall of Names during a candlelight memorial to the passengers and crew of United Airlines Flight 93 in Shanksville, Pennsylvania, the United States, Sept. 10, 2021. Memorials were held at the Flight 93 National Memorial in Pennsylvania to mark the 20th anniversary of the Sept. 11 attacks.(Photo: Xinhua)

People place lanterns at the Wall of Names during a candlelight memorial to the passengers and crew of United Airlines Flight 93 in Shanksville, Pennsylvania, the United States, Sept. 10, 2021. Memorials were held at the Flight 93 National Memorial in Pennsylvania to mark the 20th anniversary of the Sept. 11 attacks.(Photo: Xinhua)

People visit the Wall of Names during a candlelight memorial to the passengers and crew of United Airlines Flight 93 in Shanksville, Pennsylvania, the United States, Sept. 10, 2021. Memorials were held at the Flight 93 National Memorial in Pennsylvania to mark the 20th anniversary of the Sept. 11 attacks. (Photo: Xinhua)