21．一Who is knocking at the door?
一 ____ Mike.
A．That’s B．This is C．It’s D．I’m
22．In the dark street，there wasn’t a single person ______ she could turn for help．
A．that B．who C．from whom D．to whom
23. Guangdong lies the South of China.
A、in B. on C. to D. off
24. I think ______ is foolish of you not to follow his advice.
A. it B. this C. that D. one
