The correct answer is the Helsinki Accords.
The Nuclear test ban treaty was a document signed by Kennedy that forbid testing of nuclear weapons except if it took place underground.
SALT II was the strategic arms limitation treaty signed by President Carter and the leader of the Soviet Union. This reduced the amount of weapons that both countries possessed.
The Truman Doctrine was focused on giving financial assistance to countries that were in jeopardy of falling to communism. In this doctrine, Truman asked Congress to give $400 million in aid to the countries of Greece and Turkey.
This shows that the Helsinki Accords can be the only correct answer.