B. Information provided by spies in the United States.
Explanation:
The time during World War II was a very important time for developing and using nuclear capabilities. Many countries and powers believed that by obtaining new nuclear weapons and items, they would have a better chance at winning the war.
The Manhattan Project was a huge project by the United States that helped develop some of the first ever made nuclear weapons. Numerous scientists worked on this and it took some time to complete. The Manhattan Project eventually lead to Japan surrendering because of the nuclear bombs that the United States used on them.
During the Manhattan Project, numerous Soviet Union spies would use the information from the United States to create and use their own nuclear weapons. Klaus Fuchs was a very important figure in this, as he would spy and steal information from the United States and other Allied powers to help the Soviet Union.
