Question

it took him ten years to complete it. that's how long____to do it.

1 he took 2 him took 3 took him 4 he was taken
选择哪一个，及分别说出每个为什么对与错

Answer 1

选1，it taker(took) Sb ...to do sth,意为做某事（to do sth）话费了某人多少时间，你所出题目的第一句刚好就是一个例子。
所要填空的句子是个表语从句，意思是“那是花了他多少时间来完成它”本来应该是“he took how long to do it"因为做了表语从句，所以将how long提前，充当领导词，所以选1。

Answer 2

选4。
这道题是这样的，it takes/took sb......to do sth. 是做某事话费某人多长时间（一般指话费时间）。
正常情况下，空的部分应该填 it took him.
但是这里没有，所以应该用它的被动语态形式，这件事话费他时间，那么他应该是被话费时间，所以选第四个，明白？