Hey there! Your answer is: A. They were all physicists working on proving the existence of electrons
Answer:
The three men were physicist who worked in Manhattan Project.
Explanation:
Manhattan Project was a research and development undertaking promoted by United States Army with the objetive of being the first country which develops a nucelar bomb. This project was executed during World War II fearing enemies were already developing nuclear weapons, this is Why US Army Corps of Engineers worked with a group of very well known physicists of that time, for instance, Enrico Fermi, Niels Bohr and Robert Oppenheimer who was the director of the Los Alamos Laboratory.