Answer:
He believed that Germany was trying to develop one, is the right answer.
Step-by-step explanation:
President Franklin D. Roosevelt accepted a letter written by Albert Einstein on 11th October 1939. In this letter, he explained a new area of physics that represented that uranium could share atomic fission with the resultant discharge of a surpassing amount of energy. His doubts about the very fact that Germany would have started the investigation in the same field and already checked the shipping of uranium from the mines of Czech in its newly gained territory, made Roosevelt worry. Therefore, Roosevelt approved the development of the atomic bomb because he believed that Germany was developing a similar weapon.