Describe how americans responded to the terrorist attacks of 11 2001

Military action in Afghanistan was the United States response to the terrorist attacks of September 11, 2001. The correct option among all the options that are given in the question is the last or the fourth option. On the very date of 7th October 2007, the United States started the war in Afghanistan. The main target of the war was the destruction of Al Qaeda. 

Sector is best defined as (part).