Final answer:
The United States aimed to prevent the spread of communism in Cuba.
Step-by-step explanation:
The best conclusion supported by the headlines is option a. The United States aimed to prevent the spread of communism in Cuba.
The headlines mention Fidel Castro becoming the communist leader of the island, Kennedy ordering the Bay of Pigs invasion, and the U.S. using a naval blockade to prevent missiles from reaching the island. These events indicate that the United States had concerns about the rise of communism in Cuba and took actions to prevent its spread. The Bay of Pigs invasion, in particular, shows the U.S.'s active military involvement in Cuba to counter the communist regime.