what was it ____caused the forest fire?a)who b)that

问题描述:

what was it ____caused the forest fire?a)who b)that
请问为什么选B

选b.这是强调句型中的对疑问词强调.
用强调句型:“It is(was)+被强调的部分+that(who)+原句其它部分”
强调疑问词:疑问词+is(was)it +that +原句其它部分
例如:What is he doing?
What is it that he is doing?