It refers to the Soviet Union's efforts to block itself and satellite states under it from any contact with the West and its allied states.
Explanation:
The iron curtain was an imaginary line that divided Europe into two different areas of ideology and political influence beginning from the end of the Second World War (1945) to the end of the Cold War (1991).
The term specifically refers to the Soviet Union's (USSR) efforts to block itself and satellite states under it from any contact with the West and her allies. Countries that existed on the east side of the Iron Curtain were countries that were influenced by the Soviet Union. On the other hand, countries which existed on the west side were countries that were members of NATO.
The answer is D. A set of diary entries written by generals who planned strategies during world war II. This is a primary source which was written during that time period and so would be the best support for the authors' argument..
