【推荐1】It was such a serious mistake, ________ caused by carelessness.

A．which I think was	B．which I think it was
C．I think which was	D．I think which it was

【推荐2】— Tom hasn’t come to class yet？
— What do you think ________?

A．did happen to him	B．has happened to him
C．he happened	D．he has happened

【推荐3】The pen I _____ I_______ is on my desk, right under my nose.

A．think...lost	B．thought...had lost
C．think...had lost	D．thought...have lost

【推荐1】Couples in China are allowed to have three children, ________, in my opinion, is helpful in dealing with the problem of the increasingly aging population.

A．that

B．who

C．what

D．which

【推荐2】There were no other houses beyond her garden, ________ made it seem like her house lay at the end of the world.

A．which

B．that

C．where

D．what