请教有关英语中数字单位的用法.

dozen,score,hundred,thousand,million用法要点
这些词的用法极为相似,需注意的用法有：
1.当这些词与具体数字连用时,通常不加复数词尾-s,也不后接介词 of.如：
I want three score eggs.我要60只鸡蛋.
He is a man of three score years.他六十岁.
Two hundred (thousand) students went there.有两百(千)学生去了那儿.
About three million workers were on strike.参加罢工的大约有三百万工人.
注：有人认为 score,dozen 之后有时也接 of,但惯用法认为省略 of 则常见.
另外,当 million 用作中心词(即其后不接名词或数词)时,有时也可带复数词尾-s.如：
The population of New Zealand is now three million(s).新西兰现有人口三百万.
2.当这些词不与具体数字连用,而是表示不确定的泛指数时,则不仅要加复数词尾-s,而且要后接介词 of,然后才能接名词.如：
I’ve read it dozens (scores) of times.我读过它几十次.
Thousands of students entered the contest.数千名学生参加了这次比赛.
Millions of people died in the war.有数百万人在这次战争中丧生.
注：若不出现名词,则不用介词 of.如：
Millions (of people) are homeless.千千万万的人无家可归.
3.当这些词与 a few,several,many 等数目不很具体的词连用时,带不带复数词尾 -s 均可,但是注意：若不带复数词 -s,其后的介词 of 可以省略；若带复数词尾-s,则其后介词 of 不能省略.如：
在那儿我见到了数百外宾.
正：There I saw several hundred(s) of foreign guests.
正：There I saw several hundred foreign guests.
注意 some hundred persons 与 some hundreds of persons 含义不同：前者指“大约一百人”,其中 some＝about a；后者指“几百人”.
4.当这些词后面的名词有了 the,these,those等特指限定词修饰时,或其后的接的是 us,them 这样的人称代词时,则此时必须用介词 of.如：
two dozen of them 它们中的两打
three scores of these eggs 这些鸡蛋中的三打
five hundred of the workers 这些工人中的五百人
5.注意以下与介词 by 连用的例子(from www.yygrammar.com)：
The eggs are sold by the dozen.鸡蛋按打出售.
The ants arrived at the picnic by the hundred(s).成群的蚂蚁来到野餐的地方.
They were sold by the thousand(s).它们被大批大批地(论千地)出售.
比较：Pack them in dozens.把它们成打地包起来(即每12个一包).