The correct option is B. The most likely reason why President Truman ordered the atomic bomb dropped on Japan was to force Japan to surrender to the Allies.
President Truman believed that without the bomb, the U.S. was unable to claim the victory of the war. As a result, the decision to drop the bomb on Japan, even though it was difficult for Truman to decide whether to drop it or not, was made seeking for Japan's surrender. Germany had already surrendered, so they wanted Japan to surrender to end the war.
