20．-Shall I lock the lab now before I go home?

　　 --- 　　　　　. I’ll check it myself later.

　　　 A．Go ahead　　　　　 B．No problem　　　 C．No hurry　　　　　 D．Don’t bother

19．Steven’s exam results put him _________ the top ten students in his grade.

　　　 A．among　　 B．between　 C．in　　 D．at　　

18．I need to call my friend David _________ coat I walked off by mistake yesterday.

　　　 A．in whose B．in that　　　 C．with which　　 D．with her　　

17．-I did very well in the English exam last week.　

　　　 -I did _________ . I got a full mark.

　　　 A．no better B．not better　　　 C．no worse　　　 D．even worse