dozen与数词，many,several连用时，复数不加s
1.1打(a set of dozen)=12个 a dozen eggs(two dozen eggs/some dozen (of) people
2.A dozen and half=one and a half dozen
3.dozen 前有基数词表示确切数字时一般不与of连用
4.但dozen后的词有the his their 等限定词修饰时，要用dozen of (two dozen of my books)
5.dozens 几十，许多，大量 for dozens of year 好几时年以来
6.dozens of 几十的，多数的 i've been there dozens of time
7.a dozen/two dozen 不加s

先下了，正好用，谢谢了。