The correct answer is C.
The Iron Curtain was the term used to refer to the border located in the middle of the European continent that divided Europe and the whole world into two areas, since the end of WWII in 1945 until the end of the Cold War in 1991.
The territories located on the east of the Iron Curtain were the Soviet Union and its satellite states, or states under its influence. On the other hand, the states located on the west side of the border were democratic and capitalist countries, the US and its allies, and also neutral countries.
This term became popular during the Cold War era because Winston Churchill used it during a speech to refer to the division of the world in two sides.