The correct answer is Option C) Both countries felt that their rival was planning to take over the world.
The United States and the USSR were allies during World War II and their combined strenght was paramount in the defeat of Japan, Germany and Italy.
However, at the end of the War, most of the world was left devastated and there was a huge vaccum of power left due to the collapse of tradtional European powers.
The United States and the USSR, both of which emerged as two most powerful political entities, then sought to influence and control the world.
The USSR believed that the United States would likely try to influence world politics, while the United States had similar feelings for the USSR.
This eventually turned into a rivarly called the Cold War. While most analyst assume that the Cold War ended with the collapse of the USSR, there is renewed tensions between the US and Soviet Union's successor, Russia.