Question

in 1945, what concern did the allies have about invading the japanese mainland with ground forces?
they were worried they did not have enough soldiers.
they were worried there would be too great a loss of life.
they were worried the japanese were developing an atomic bomb.
they were worried the japanese had a stronger fleet in mainland ports.

Explanation:

In 1945, the Allies estimated that an invasion of the Japanese mainland would lead to a very high - number of casualties on both sides due to the fierce resistance expected from the Japanese military and civilian population. There was no evidence that Japan was close to developing an atomic bomb at that time, and the Japanese fleet was severely weakened. The main concern was the high loss of life.

Answer:

They were worried there would be too great a loss of life.