Question

Which term refers to a nation's tendency to expand its armed forces and acquire new and better weapons?

Answer 1

The correct answer in this case would be militarism (b). The reason why this is the correct answer because a nation's tendency to expand its armed forces and acquire new and better weapons is also exactly that - militarism. 

Other answers here wouldn't be correct because they have different meanings. The only thing that would come close is imperialism which has some similarities but is used in different contexts.