If you googled it, you would find that this question has already been answered here:
http://answers.yahoo.com/question/index?qid=20101212172404AAkT3A6
B: Detente...
However, I think all of these answers could be right, in a way. Depends on if you can justify your answer or not. Ask your teacher to explain exactly what the heck she's talking about in plain english you can understand... if you have to come here to look for answers, she or he or it isn't doing their job very well, IMHO.
I'm not sure that you understand what the cold war was, but then again, I don't anyone really does. Why is your teacher using multiple-choice anyways? Look for adults who really know their history and how to talk about in a way that is interesting to you and makes sense.