The correct answer is D) the two countries changed from being friendly allies to being fierce rivals.
The way in that the relationship between the United States and the Soviet Union change after World War II was "The two countries changed from being friendly allies to being fierce rivals."
During World War II, The United States were allies. If not so friendly, both countries had a decent relationship and fought for similar interests in the region. The other two big allies were France and Great Britain.
However, after World War II, the United States and the Soviet Union became fierce and permanent rivals in what was known as the Cold War years, in which, the USSR and the US rivaled and competed in the arms race and the space race.