下列各句中，没有语病的一项是（ ）

There is somebody knocking at the door.Who________ it be—I’m not sure. It ________ be a postman.

o cause people some health problems, in fact farmore serious _____ than computers do

She feels unhappy, _____?

. — If I were you, I would have accepted the job. — I ___________ the offer because it would mean frequent business trip away from my family,