The correct answer is B. 2001.
On September 11, 2001, 19 militants associated with the Islamic terrorist group al-Qaeda hijacked four airplanes and carried out suicide attacks against targets in the United States. Two of the planes were flown into the twin towers of the World Trade Center in New York City, a third plane hit the Pentagon just outside Washington, D.C., and the fourth plane crashed in a field in Shanksville, Pennsylvania. Nearly 3,000 people were killed in the attacks, which triggered major U.S. initiatives to combat terrorism and defined the presidency of George W. Bush.
Option A is incorrect because the year 2000 was a year before the September 11 attacks.
Option C is incorrect because the year 2002 was a year after the September 11 attacks.
Option D is incorrect because the year 2003 was two years after the September 11 attacks.