Question

why is september 11, 2001, a significant date in us history?
al - qaeda carried out the largest terrorist attack against the united states on this date.
it is the date that congress passed the patriot act authorizing sweeping surveillance powers.
it is the date that the us military launched a \war on terror\ in iraq and afghanistan.
al - qaeda leader osama bin laden was killed on this date by us military forces.

Explanation:

On September 11, 2001, al - Qaeda hijacked four commercial airliners and carried out terrorist attacks in the US. The Patriot Act was passed later, the "war on terror" was launched after 9/11 but not on that exact date, and Osama Bin Laden was killed in 2011.

Answer:

Al - Qaeda carried out the largest terrorist attack against the United States on this date.