Answer:
D. Castro began developing ties with the USSR, which was America's major opponent during the Cold War.
Step-by-step explanation:
The emergence of Fidel Castro as the sole supreme leader of Cuba would become one of the harshest and most devastating events in the history of Cuba. By overpowering the current leader General Fulgencio Batista, Castro established himself as a capable leader to save his people.
The U.S. at first supported Castro and even invited him to the U.S. But merely a year into his leadership, Castro called upon the Soviets and its military advisers into Cuba. alarming the U.S. Moreover, Castro also made "decisions that, he must have known, would antagonize the U.S." This would become one of the initial causes of the hostility between the United States and Cuba.
Thus, the correct answer is option D.