21. The sign reads “In case of ______ fire, break the glass and push ______ red button.”
A. 不填; a B. 不填; the C. the; the D. a; a
22. I am afraid Mr. Wang ______ see you now. He is on a business trip.
A. can’t B. mustn’t C. needn’t D. shouldn’t
23. —Miss Smith is in hospital.
—Oh, really? I ______ know. I will go and visit her.
A . don’t B. didn’t C. do D. did
