a) containment
Containment was the policy of halting the spread of communist influence across the world. During the cold war this was an response the the Soviet Union attempting to enlarge communist influence in Eastern Europe and Asia. Its importance to the US was that it lead to the involvement of the US in the Korean War and the Vietnam War. The policy of containment lead to more US involvement in foreign conflicts.
c) détente
This was the easing of political tension between the US and the USSR. This period was defined by the signing of several treaties between the two powers in order to reduce the danger of nuclear war. This was important as it lead to several trade agreement and several nuclear non-proliferation agreements, as well as a reduction in the stockpiles of nuclear arms.