How dose americas pre world 2 isolationism relate to a discussion of the marshall plan, the berlin airlift and nato?

In 1947, President Harry S. Truman pledged that the United States would help any nation resist communism in order to prevent its spread. His policy of containment is known as the Truman Doctrine.The Truman Doctrine demonstrated that the United States would not return to isolationism after World War II, but rather take an active role in world affairs.To help rebuild after the war, the United States pledged $13 billion of aid to Europe in the Marshall PlanThe world was in flux in the aftermath of World War II, and political upheaval reigned in many countries. Already wary of communism thanks to George Kennan's Long Telegram, the United States was dismayed when a number of countries in Europe and Asia adopted communist governments in the late 1940s.When England notified the United States that it could no longer afford to fight communist insurgencies in Greece and Turkey, US President Harry S. Truman issued what would become known as the Truman Doctrine: a promise that the United States would do whatever was necessary both economically and militarily to contain the spread of communism AROUND THE WORLD 

The answer is option a. boundary line drawn by pope alexander iv in 1493.