We want to know what it was____caused the accident.

题目

We want to know what it was____caused the accident.
A.when B.how C.that D.where
一定要把对错理由讲出来

答案

选C.这是it was...that的强调句型.
句子不缺少主语或者状语成分,所以不用when,how或者where.