题目内容
—How dirty the river is!
—But it ____ quite clean before a paper factory ____ set up there.
A. will be; was B. is; / C. has been; / D. used to be; was
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题目内容
—How dirty the river is!
—But it ____ quite clean before a paper factory ____ set up there.
A. will be; was B. is; / C. has been; / D. used to be; was