"The Truman Doctrine Marked a New Level of American Commitment

"The Truman Doctrine marked a new level of American commitment to a cold war."On what basis is this statement made?

A) The Truman Doctrine for the first time committed the U.S. to a peacetime military alliance.
B) Truman publicly and finally rejected Stalin's offer of friendly negotiations between onetime allies.
C) Truman's pledge to support free peoples who resisted totalitarian takeover signaled an open-ended intent to oppose the Soviets anywhere in the world.
D) Sending military advisers to Greece was the first step in U.S. involvement in the Middle East quagmire.