All these occurred in the u. s. during the cold war except
(a) build-up of military arms
(b) interrogations of citizens
(c) protection of free speech
(d) fear of nuclear war

C) The protection of free speech, is the correct answer.

Within the US, the Cold War was a state political and military tension after WWII, based on the threat of nuclear war, so D is not the answer. As well, McCarthyism was a product of the cold war and was characterized by investigating citizens on the charges of treason, so B is not the answer either. The arms race is another characteristic of the Cold War, due to the military tension of the cold war, therefore A is not the answer either. That leaves C as the correct answer, which makes sense considering the prevalence of McCarthyism during the era.