this is bbc news, the headlines: sombre ceremonies have been taking place in the united states to mark 20 years since the september 11 attacks, when al-qaeda hijackers used airliners to kill almost 3,000 people. in new york, president biden urged people never to forget the deadliest attack on us soil. in pennsylania, where another plane crashed after passengers tackled the hijackers, the former president george w bush warned of the new danger of domestic extremism. the 9/11 attacks led to us troops invading afghanistan. the british 18—year—old, emma raducanu, has won the us open, in one of the most dramatic victories in modern tennis. she beat 19—year—old leylah fernandez of canada in two sets, six—four, six—three. raducanu only made it into the tournament as a qualifier.