关于句子里 which 和 it?

Question

I cannot imagine any circumstances under which it would be useful or fruitful to announce some new drive for a comprehensive peace settlement. (此处，which我理解为关系代词，代后面的整个从句；后面从句又包含一个从句，而it代从句中to所引不定式的作主语。不知道我理解的是否正确？望给予指正！谢谢。)

Answer 1

which为关系代词，指代ny circumstances，在后面的定语从句作under的宾语。而在定语从句中it代从句中to所引不定式的作主语 正确.

可以看出你的英语还是不错的.
希望对你有帮助.

Answer 2

under which = under any circumstances
so your example can change to: I cannot imagine under any circumstances would be .... You see, if put under in front of any, delete which it, the sentence is still intact.来自：求助得到的回答

Answer 3

对吧应该！！which引导的应该是一个介词under引出的一个名词性从句，it 为形式主语，for后为补充成分。
所以我感觉你的分析不错！追问

也很感谢你的帮助，但只能采那位最快回答的朋友了，真心感谢！