the date of an attack in 2001 in which two airliners were flown directly into the World Trade Center, causing the complete collapse of the twin towers, and a third airliner was flown into the Pentagon, causing a five-storey section of the building to collapse; a fourth airliner, believed also to have been targeted on Washington, was brought to the ground in Pennsylvania as a result of what is thought to be passenger intervention. The airliners were hijacked by Islamic fundamentalist terrorists believed to be involved with Al Qaeda. Known in the US as 9/11.
九一一事件（2001年9月11日发生的袭击事件, 两架客机直接撞入纽约世界贸易中心大楼, 致使该双子塔完全倒塌; 第三架客机撞入五角大楼, 导致该建筑一五层侧楼倒塌; 据信第四架客机也以华盛顿为攻击目标, 但估计因乘客阻止, 在宾夕法尼亚州迫降; 这些客机被伊斯兰原教旨主义恐怖分子劫持, 人们相信这些恐怖分子和基地组织有联系; 美国称9/11）。