911事件英文讲述

The September 11 attacks (often referred to as September 11th or 9/11) were a series of coordinated suicide attacks by al-Qaeda upon the United States on September 11, 2001. Four commercial jet airliners where two of it were being crashed into the Twin Towers of the World Trade Center in New York City, another jet into the Pentagon in Arlington, Virginia, just outside Washington, D.C., and the fourth plane crashed into a field near Shanksville in rural Pennsylvania. 2,973 victims and the 19 hijackers died as a result of the attacks.The overwhelming majority of casualties were civilians, including nationals of over 70 countries.

‘911事件’的原因是什么？