Itcantakeaslongaseightdaystorigupropeladdersandtoestablishsupplybasesbeforeadescentcanbemadeintoaverydeepcave.it指什么,这是什么类型的形式主语不用it怎么翻译?beforeadescentcanbemadeintoaverydeep

Question

It can take as long as eight days to rig up rope ladders and to establish supply bases before a descent can be made into a very deep cave.
it 指什么,这是什么类型的形式主语
不用it怎么翻译?before a descent can be made into a very deep cave can take as long as eight days to rig up rope ladders and to establish supply bases
make a descent into ...这是词组吗，
句子成分是什么这句？

Answer 1

it 作为形式主语代替后面的动词不定式,这个句型是It takes +多长时间+to do sth.表示做某事要花费多少时间.
后面那句before从句前置,但it不能省略,必须用啊!
在这句话中make a descent不能算是词组.是说在地面下陷形成一个非常深的洞穴之前,只要花八天的时间就能搭起绳梯并且建立供应基地.