先看试题：
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
1.当与具体的数字连用的时候，不用复数，且后面不用介词of,如：
four dozen eggs四打鸡蛋（48个鸡蛋）
Only about half a dozen people turned up.
只有六七个人到场。
There was only space for a half-dozen tables.
只有摆六张桌子的地方。
You will be able to take ten dozen bottles free of duty through customs
你可以携带120瓶免税通过海关。
He had two dozen oysters and enjoyed every one of them.
他吃了两打牡蛎，每一只都吃得津津有味。
He sat behind a table on which were half a dozen files.
他坐在一张放有6个文件夹的桌子后面。
2. dozens of 名词复数，许多，大量，几十个
dozens of times.
I've been there dozens of times.
我到那里去过很多次。
She’s got dozens of boy-friends. 她的男朋友很多。
Dozens of doctors and nurses have been working day and night for weeks
很多医生和护士已经夜以继日地工作数周了。
Dozens of miles of railway track have been torn up
好几十英里的铁轨被毁坏了。
He said there were dozens of economic plans in the works
他说有几十项经济计划已经开始实施。
Dozens of villages have been razed
几十个村庄被夷为平地。
Most office buildings have dozens of air ducts and vents.
多数办公楼都有许多的管道和通风口。
By borrowing from dozens of banks, he managed to avoid giving any of them an overall picture of what he was up to
他向许多银行借款，使得任何一家都搞不清楚他到底要做什么。
Bad weather has caused dozens of flight cancellations over the holiday weekend.
恶劣的天气已经导致这个连假周末数十个航班被取消。
3.当a few,several,many，some等数目不很具体的词连用时，有两个中形式：
这些词 dozen(of) 名词复数
这些词 dozens of 名词复数
表示很多、许多、几十个等
此时dozen不加复数词尾-s时，其后的介词of可以省略;加词尾-s时，其后介词 of不能省略。
如：several dozen (of) eggs=several dozens of eggs许多鸡蛋
several dozen (of) pencils=several dozens of pencils几打铅笔
Several dozen councillors walked out of the meeting in protest
几十名政务会委员愤然从会场退席以示抗议。
4.当后面的名词有the,these,those等特指限定词修饰时，或其后接的是them,us等这样的人称代词时，则此时必须有of , 注：score, hundred, thousand, million等也具有以上类似用法。如：four dozen of these eggs四打这种鸡蛋
I want five dozen of these eggs.
我要五打这种鸡蛋。
He ordered a dozen of their best red roses
他订购了12朵他们那儿最好的红玫瑰。
常见考点形式有三：
基数词、many,several, dozen 复数
基数词 dozen of sb或the\these\those\one’s 复数
Dozens of 复数
5.in dozens,大批的，成打的
They arrived in dozens (= in large numbers) .
他们大批到达了。
Pack them in dozens.
把它们成打包装起来。
以上基数词都是除了a 以外。
I had bred a dozen of chickens.我饲养了12只小鸡。
He ordered a dozen of their best red roses
他订购了12朵他们那儿最好的红玫瑰。
上题最佳答案为C。
