—What"s behind the door?—There must be a dog _____ behind it. [ ]A. to sit

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—What"s behind the door?
—There must be a dog _____ behind it. [     ]
A. to sit
B. sit
C. sitting
D. to sitting

答案

举一反三

Your donation is greatly _____. [ ]
A. appreciate
B. appreciating
C. appreciated
D. being appreciated

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I heard someone        _ with my father in the next room at ten last night.             [     ]
A. talk
B. talking
C. to talk

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Teenagers aren"t _________ to get their ears _____.      [     ]
A. allow; pierce
B. allowed; pierce
C. allowed; pierced

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They just walk around the town center,        many of their friends.             [     ]
A. see
B. seeing
C. seen

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In China, it"s rude to talk while        .               [     ]
A. eat
B. to eat
C. eating

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