The earth(地球) is our home, and we must _____ it clean.
All of us find __________ difficult to do the exercise. A. this B. it C. that
I don’t think he can read the new words so well, __________? A. can he B. can’t he C. do you
—Must I come before 7:00 tomorrow? —No, you ________. A. needn’t B. mustn’t C. couldn’t
Our teacher often uses the Internet ________ he often sends emails. A. or B. and C. but
My teacher is a friend of _________. A. mother’s of Jim B. Jim mother’s C. Jim’s mother’s