________ troubles him is the thought ________ .

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A．That, that they broke the rule

B．That, which they broke the rule

C．What, that they broke the rule

D．What, which they broke the rule

Father made a promise ________ I passed the examination he would buy me a bicycle.

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________ I was free that evening.

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________ we'll go camping tomorrow depends on the weather. 

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________ she couldn't understand was ________ fewer and fewer students showed interest in her lessons. 

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

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________ I can't understand is ________ he wants to change his mind.

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________ matters little.

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It ________ that space is limitless.

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After a whole day of hard work, all ________ was a nice meal and a good rest.

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