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

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. dozen; dozen

答案：

A. dozen of ; dozen

B. dozens of ; dozens

(答案→)C. dozens of ; dozen

D. dozen; dozen

解析：考察固定用法。Dozens of许多，大量；dozen前面有数词时，接dozen原形。故C正确。句意：我们已经有了很多铅笔，但是我们还需要2打钢笔。