The correct answeer is D., The Truman Doctrine.
The Truman Doctrine was the United States policy designed to handle the threat of communism spreading the Middle East during the decade of the 50s.
President Truman addressed the Congress on March 12, 1947. The result of that speech was what was known as the Truman Doctrine. Truman asked Congress to help the government of Grace to fight Communists Greek Party. The U.S also helped Turkey
The U.S. government thought that Russia could spread Communism through those countries.