问题描述：
The present population of this city is three times（ ）it was ten years ago.
The present population of this city is three times（ ）it was ten years ago.A.what B.since C.that D.as 正确答案是A,为何不选C?
The present population of this city is three times（ ）it was ten years ago.A.what B.since C.that D.as 正确答案是A,为何不选C?
问题解答：
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