34. The lake used to be polluted but now something to make it clear again.A. is being don

问题补充：

34. The lake used to be polluted, but now something to make it clear again.

A. is being done

B. does

C. is doing

D. is done

答案：

(答案→)A. is being done

B. does

C. is doing

D. is done

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