We have sometimes accidents on this line, but no accidents ______ since last winter.
A. occur
B. have occurred
C. have been occurring
D. are occurring
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He _____ on this essay for twenty minutes but he _____ only a hundred words.
A. has been working/has written
B. is working/writes
C. has worked/has been writing
D. works/is writing
Elections _______ every four years and Congress meets once a year.
A. are taken place
B. are to be taken place
C. took place
D. take place
______ careless, or you will make mistakes.
A. Be not
B. Not be
C. Don’t
Don’t be
The No.8 bus ______ to Chengdu college of Geology, and not to Sichuan University.
A. are gone
B. is being gone
C. goes
D. are going
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