The correct answer is to stop the spread of communism.
After World War II, the US and Soviet Union emerged as global superpowers. They also emerged as rivals, as the US and Soviet Union had two completely different economic and government systems. With this in mind, the US took multiple steps to stop the spread of communism, the political/economic system that the Soviet Union used at this time.
The Truman Doctrine attempted to stop the spread of communism by giving aid to countries that were in danger of falling to communism. This law gave $400 million to the countries of Greece and Turkey. The policy of containment, on the other hand, focused on stopping the spread of communism all over the world.