21．She is _____ newcomer to _____chemistry but she has already made some important discoveries.
A. the; the B. the; / C. a; / D. a; the
22. — Shall we go and have a picnic at the weekend?
— ______. According to the weather forecast, there might be a cold front by then．
A. Why not B. We can wait C. No, let's not D. It depends
