Which of the Following Was a Key Factor Contributing to the Development

Which of the following was a key factor contributing to the development of the Cold War in Eastern Europe?

A) The withdrawal of victorious Russian armies from lands conquered during the campaign against Nazism
B) Raids by American troops pursuing German Nazi war criminals into areas of the former Third Reich under Russian control
C) Stalin's desire to establish pro-Soviet governments in the countries of Eastern Europe to serve as a buffer zone against possible Western attacks on the Soviet Union