B is correct. Unterseaboats, the German word for submarines, sunk many Allied merchant ships and eventually the allies started protecting their ships with convoys of military ships that were only slightly effective until anti-submarine technology improved.
It came from Italy there was the first one to create it
Policy of containment
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.
USA is the correct answer