1. A primary reason for Truman's decision to drop the atomic bombs on Japan was that he thought that it would lead to less deaths than a land invasion. The correct option is option "A".
2. "The Allies were afraid that the technology would be stolen by spies belonging to Germany or Japan" is the reason why the Manhattan Project was kept top secret. The correct option is option "C".
3. The Three Non-Nuclear Principles were intended to keep Japan from ever developing or using nuclear weapons. The correct option is option "C".