What major event happened on September 11, 2001 in the United States?

Question

Accepted Answer

Terrorists attacked the United States; Terrorists took over two planes and crashed them into the World Trade Center in New York City; Terrorists took over a plane and crashed into the Pentagon in Arlington, Virginia; Terrorists took over a plane originally aimed at Washington, D.C., and crashed in a field in Pennsylvania

115. 2001年9月11日在美国发生了什么重大事件？

为什么