what made allied leaders worry about the cost of invading the japanese mainland?\n○ kamikaze fighters\n○…

Answer:

A. kamikaze fighters

Brief Explanations:

Kamikaze fighters were Japanese suicide - attack aircraft. Their attacks were expected to cause high casualties and damage during an invasion of the Japanese mainland, worrying Allied leaders about the cost of such an invasion. Machine guns, atomic bombs, and warplanes were not what specifically made Allied leaders worry about the cost of invading the Japanese mainland in this context.