How did congress respond to the september 11, 2001, terrorist attacks?
by declaring war on afghanistan
by reducing funding for the cia
by strengthening economic sanctions against iraq
by creating the department of homeland security

It was September 11, 2001 when the United States was attacked by terrorists.] Three planes crashed into the strategic buildings in the United States. The Congress responded to the September 11, 2001, terrorist attacks by declaring war on all terrorist groups and invaded Afghanistan. 

Thus, the answer to this item is the first option, by declaring war on Afghanistan.