Answer:
A. In 1950, the United States and the Soviet Union were two of the most powerful countries in the world.
Step-by-step explanation:
This is the sentence that best states the thesis. The main thesis should state that the United States and the Soviet Union were two of the most powerful countries in the world because the details that follow support this statement. The student tells us that both countries ruled large areas of land, and that both possessed many destructive weapons, which means they both were quite powerful.