How and why were the cold war geographic boundaries drawn?

The correct answer is the following.

The geographic boundaries in the Cold War were dictated at the end of the 1940s, due to the Cold War between the Soviet Union and the United States. The Soviet Union wanted to spread Communism in many parts of the world. In opposition, the United States wanted to prevent the spread of Communism around the globe. After the Yalta Conference and the Potsdam Conference, the leaders of the United States, Great Britain, and the Soviet Union had agreements to be followed after World War II, but the real thing was that the global division of power changed considerably to the degree that the Soviet Union controlled Eastern Europe countries such as Hungary, Romania, Poland, and Bulgaria. Communism also reached China, Vietnam, and Cuba.  

i think the answer is a and i hope this ; ))