Former U.S. President Barack Obama (1st L, C), his wife Michelle Obama (2nd L, C), U.S. President Joe Biden (3rd L, C) and his wife Jill Biden (4th L, C) attend a commemoration ceremony of the 20th anniversary of the 9/11 attacks in New York, the United States, on Sept. 11, 2021. The commemoration ceremony was held here on Saturday to mark the 20th anniversary of the 9/11 attacks. (Xinhua/Wang Ying)
