The correct answer is B. He had firsthand knowledge of the destructiveness of the bomb.
Explanation
Julius Robert Oppenheimer (1904-1967) was an American physicist who was highlighted for his contribution to the construction of the Atomic Bomb through his participation in the Manhattan Project. This plan was carried out by the United States during World War II to develop the first nuclear weapons in history. However, sometime later when the atomic bombs were dropped on the Japanese cities of Nagasaki and Hiroshima Oppenheimer openly expressed his opposition to this decision because as a collaborator in the manufacturing process of those bombs, he knew how destructive they were, and the harm to innocent people that they would cause. Therefore, the correct answer is B. He had firsthand knowledge of the destructiveness of the bomb.