We already have pencils but we need two pens.A. dozen of dozenB. dozens of dozens C.

问题补充：

We already have pencils, but we need two pens.

A. dozen of, dozen

B. dozens of, dozens

C. dozens of, dozen

D. dozens of, dozen of

答案：

A. dozen of, dozen

B. dozens of, dozens

(答案→)C. dozens of, dozen

D. dozens of, dozen of

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