Answer:
D is the right answer. After almost 30 years, China and the United States went back to having normal relations.
Nixon and Kissinger used triangular diplomacy to try to make things better between the US, the USSR, and China. The policy's main goal was to keep the balance of power in the world and keep any one country from becoming too powerful.
Option C isn't right because, even though the United States and the Soviet Union did talk about anti-ballistic missile treaties at this time, that wasn't the main point of triangular diplomacy. The US and the Soviet Union were able to get along better because both countries tried to make peace.
Option A is not the right answer because some of the goals of triangular diplomacy were met, especially with China.
Option B isn't right because triangular diplomacy wasn't used to do either of the other two things.