What was the main purpose of Truman's speech

Question

a)to frighten the soviet gobernment
b)to make clear how the United States would respond to Communist aggression c) to win congressional approval of the containment policy d)to expand the cold war

Answer 1

a is silly with the word "frighten"
b the policy was to me unclear, it just said we would support...
c. Robert Taft was a leader in the Senate, and he was a blue blooded Isolationist, Trumans speech put pressure on him.
d. this started the cold war, not expanded it.

Answer 2

So C is correct..?