一道英语单选,

问题描述:

一道英语单选,
( )that caused our younger daughter to fail in the important exam?
A .what do you think it was B.do you think what it was
C.what do you think was it D.do you think what was it
后面还有回答 carelessness

答案是a,这是主语从句和表语从句的结合 what do you think it为主语从句 was为谓语 that caused our younger daughter to fail in the important exam为表语从句