It is pretty well understood ________ controls the flow of carbon dioxide in and out the atmosphere today.

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________ is still unknown.

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A．When and where this took place

B．When and where did this take place

C．It was when and where that took place

D．This took place when and where

We were all overjoyed at the news ________ the experiment turned out a success.

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I don't think the number of the people ________ this happens is very large.

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Jane was the first girl ________ when you got here.

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The people in the whole city, ________, welcomed the new mayor.

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A．most of who were workers

B．most of whom were workers

C．most of them were workers

D．most of which were workers

________ is mentioned above, the number of the students in senior high schools is increasing.

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In the dark street, there wasn't a single person ________ she could turn for help.

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To get the job started, ________ I need is your permission.

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Such magazines ________ I am reading are of much value to the students.

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