21. ______ most efficient way to understand thousands of new words is to gain ________ good knowledge of basic word formation.
A．A; a B．The; 不填 C．A; 不填 D．The; the
22. — Did the door-keeper let you in?
— No. ________ I tried to tell him I was your relative, he just didn’t believe me.
A．Whether B．However C. No matter D．Even if
23. ---Michael was late for Mr.Smith’s oral class this morning.
--- _______? As far as I know, he never came late to class．
A．How come B．So what C．Why not D．What for
