The correct answer is A.
The U.S. was always afraid of the spread of communism. The country was committed to democracy and the right of the citizens to determinate their own form of government. In communist countries, free choosing of government was not possible. In 1947, President Truman pledged that the United States would help any nation resist communism in order to prevent its spread. His policy of containment is known as the Truman Doctrine.
Another reason for wanting to stop the growth of communism is the fact that the USA is a capitalistic country. Its prosperity depends on people buying its goods all over the world. In communist countries, there is no free market economy which cuts people off buying American export goods. This undermines capitalism as a economic system.
