Final answer:
George W. Bush responded to the events of September 11 by declaring a) a "War on Terror," initiating military campaigns in Afghanistan and Iraq, and enhancing domestic security measures.
Step-by-step explanation:
Following the September 11, 2001, terrorist attacks, President George W. Bush handled the situation by declaring a "War on Terror" in an address to a joint session of Congress on September 20, 2001. He demanded that the Taliban turn over Al-Qaeda leader Osama bin Laden or face attack by the United States.
This marked the beginning of military campaigns in both Afghanistan and Iraq, and was accompanied by significant domestic security enhancements, including the establishment of the Office of Homeland Security and the passage of the Homeland Security Act and the USA Patriot Act. The correct answer to the multiple-choice question would be (a) He declared a "War on Terror" and implemented security measures.