While the threat of mutually assured destruction seemed to fade with the end of the cold war, the threat of still exists.
a. the spread of communism
b. the proliferation of weapons of mass destruction
c. conflict over the colonization of underdeveloped regions
d. proxy wars between the soviet union and the united states

I don't think that right now there is a threat of the spread of Communism or of proxy wars,(options A and D are false) but the problem which is still present is the problem of proliferation of the weapons of mass distraction: especially, as they are getting cheaper and easier to produce. 
(answer B).

Also, countries no longer have colonies in the strict sense, so also option C is false