Shortly after the accident two police were sent to the spot to keep order.A. dozens ofB.

问题补充：

Shortly after the accident, two police were sent to the spot to keep order.

A. dozens of

B. dozens

C. dozen of

D. dozen

答案：

A. dozens of

B. dozens

C. dozen of

(答案→)D. dozen

解析：英语中一些表示数字的名词的前面如果用了数词，这些名词必须是单数形式，如dozen（一打），score（二十）和head（头）等，例如：另外两打鸡蛋another two dozen eggs。但是如果这些名词用来虚指某些可数名词时，这些名词呈复数形式，其后要加上介词of，例如：dozens of pencils（几十支铅笔）。