Why Was the Formation of the North Atlantic Treaty Organization

Why was the formation of the North Atlantic Treaty Organization (NATO) significant to American foreign policy?

A) The commitment to NATO as a mutual defense alliance against the Soviet Union marked an end to isolationism in the United States.
B) In keeping with the decision of the United States not to join the League of Nations, the formation of NATO indicated the return of isolationism in the United States.
C) The creation of NATO demonstrated that the United States was unwilling to go to war on behalf of its allies but factored its allies into economic decisions.
D) The establishment of NATO represented a partnership with the Soviet Union that acted as a stabilizing force despite the underlying tensions of the cold war.
E) NATO was deeply unpopular among the American people at the time of its formation and eroded popular support for the federal government in general.