The spending of enormous sums on the original bomb project was spurred by the belief that 

a. a nuclear waapon was the only way to win the war
b. the germans mmight acquire such a weapon first
c. the japanese were at work on an atomic bomb project of their own
d. scientists like albert einstein might be lost to the war affect 
e. the american public would not tolerate the casualties that would result from a land envasion of japan