英语：Could （ ） have been ( )who helped Sunny get her work done?

题目

英语：Could （ ） have been ( )who helped Sunny get her work done?
1.they ,it 2.they ,them 3.it ,them 4.it ,they
这句话什么情况 我没看明白 4是什么情况?
其他的为什么不能用 请帮我分别解释一下好么

答案

Anwer:此句是一个强调句构"It" was "they" who helped Sunny get her work done.可以看出用"it","they"一目了然.去掉"It was ...who"这个强调框架,原句为They helped Sunny get her work done.原句只不过对这个强调...