The correct answer is:
A. When Fidel Castro took power in Cuba he sought aid from the Soviet Union and put Cuba in the Soviet sphere of influence.
The Marshall Plan and Truman Doctrine were part of the broader U.S. strategy to contain communism after World War II. When Fidel Castro came to power in Cuba in 1959, he initially had some support from the U.S. but quickly turned to the Soviet Union for economic and military support, leading to Cuba's alignment with the Soviet bloc. This shift contributed to the deterioration of diplomatic relations between the United States and Cuba.