21. —Someone might see us.
—________? We are not doing anything illegal.
A. What’s up B. What if C. How come D. So what
22. —Why not open the windows to let _____ cool air in ?
—I’d rather you didn’t. _____ air in our town is terribly polluted.
A. /; The B. a; The C. /; / D. the; /
