To What Does the Term Iron Curtain Refer

To what does the term Iron Curtain refer?

A) The nickname given by Soviet officials to the new extended frontier against Western aggression in central Europe.
B) The nickname given by Soviet military officers to their blockade established around Berlin in 1948.
C) An early nickname given by NATO troops to the Berlin Wall.
D) The nickname given by Winston Churchill to the line separating Soviet-dominated Europe from capitalist Europe.
E) The code name for the naval blockade of Cuba during the Cuban Missile Crisis of 1962.