Choose the best answer which can complete the sentence.

The price of a cup of coffee ________ by ten cents.

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The research is so designed that once ________ nothing can be done to change it.

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The old couple have been married for 40 years and never once ________ with each other.

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The scholar has made another break－through in this field, ________ of great importance to the progress of science and technology.

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A．I think which is

B．which I think it is

C．which I think is

D．about which I think it is

Do you think the reason ________ he gave is believable?

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My hometown is no longer the same ________ it used to be.

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The old woman has two sons, one ________ is a teacher.

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She hasn't got enough money ________ to buy the rings.

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The scientist and his achievements ________ you told me about are admired by us all.

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Winter is the time of year ________ the days are short and nights are long.

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