The correct answer is C) the United States.
The nation that the director feared might use the weapon they had developed against the Soviet Union was the United States.
The quote of the Director referred in the question is the following: "When we succeed in resolving this problem, we felt relief, even happiness-for in possessing such a weapon, we had removed the possibility of its being used against the USRR with impunity."
It was said by the Director of the Testing in the Soviet Union. Laboratory
We are referring to the Cold War years that confronted the United States and the Soviet Union in many aspects such as the arms race to construct nuclear weapons or the spread of Communism by the Soviet Union or the measures by the United States to stop it.
