The correct answer is A) Became the basis for American foreign policy in the post-WWII period.
The containment policy of the Truman administration: "Became the basis for American foreign policy in the post-WWII period."
Here we are talking about the so-called Truman Doctrine.
The Truman Doctrine was a United States policy installed by President Harry S. Truman aimed to stop the spread of Communism in the world. It was communicated by President Truman on March 29, 1947, as part of the measures the US government was taking during the Cold War years.
George F. Kennan was an American diplomat, expert in Russian affairs because lived in Russia and knew its culture and history. He recommended the State Department to counter-attack the effects of Communism in the world because Russian leader Joseph Stalin was convinced of disrupting and attacking capitalists countries. So these ideas influenced Truman's doctrine.