Answer:
B. The United States
Explanation:
The US lead turned to be the first in developing with sucess the use of nuclear energy as a weapon of mass destruction. In cooperation with UK and Canada, it started the Manhattan project.
Manhattan project resulted in the first atomic tests that would be applied to change warfare and ultimately led to ending WW2.
The project was also able thanks to acquiring intelligence on the German nuclear weapon project. Through Operation Alsos, Manhattan Project personnel were in Europe, often behind enemy lines, where they gathered secret nuclear materials and key documents, and gathered German scientists. As the Manhattan Project's developed, Soviet spies successfully joined as well the program.
Officially, the first nuclear test ocurred at New Mexico's Alamogordo Bombing and Gunnery Range on 16 July 1945.
