16.Had(A) Aristotle asked his wife to keep her mouth open while(B) he counted(C) her teeth,he could avoid(D) the mistake of thinking that women have fewer teeth than men.
　　17.John must be(A) a restless(B) person.He kept(C) moving(D) from country to country.
　　18."Whatever you decide(A),you'll let(B) me know by phone,won't you(C)?" "Yes,Mr.Brown,I certainly must(D)."
　　19.We requested(A) that the superintendent of the building clean up(B) the storage room in the basement(C) so that the children had(D) enough space for their bicycles.
　　20.You needn't(A) have interrupted(B) the class to tell me that;you could come(C) to me afterwards(D).
　　答案：16. D (改为：have avoided）
　　17. B (改为：must have been)
　　18．D (改为：will)
　　19. C (改为：might have)
　　20. B (改为：have come)

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