Answer:
D: To bring the war in the Pacific to a quick end.
Explanation:
It's not A because first, China was a good ally for the US and really didn't care about them getting intimidated, Korea was still under Japanese control so it didn't exist, and the only true part of this answer is that in some way the US did want to show their power over the USSR.
It's not B because at that point Italy and Germany were under full ally occupation and thus they really can't do anything.
It could be C because the Americans didn't really test their atom bomb yet and I gusse they wanted to see if its atomic weapons worked but this isn't the best answer.
It is D because a mainland invasion of Japan would probably be another few millions of deaths in the stockpile since Japan planned the protection of the Home Islands a while ago. The allies did actually draw out a plan for an allied invasion of the Home Islands, you could search it up, it's called operation downfall which has two different invasions in it. And another reason it's D is because at that point half the world was suffering from war exhaustion and wanted a quick end to the Pacific war.
