Following the rise of communism in Russia there was what was called the "Red Scare" in the United States which led to anti-communist activities such as the "Palmer Raids" which were carried out by Mitchell Palmer. Therefore, A) Attorney General Mitchell Palmer used the public's fear of communism to start a witch hunt for suspected communists is the best answer.
Developed by the administration of Harry Truman in the late 1940s, the correct answer is the policy of containment.
Containment refers to the US's policy, developed by legendary diplomat George Kennan, where the US would help any free nation threatened by communism by stopping the spread of communism.
Many different factors, including the decentralized political nature of Spain, inefficient taxation, a succession of weak kings, power struggles in the Spanish court and a tendency to focus on the American colonies instead of Spain's domestic economy, all contributed to the decline of the Habsburg rule of Spain.