【基础知识】关键词：基数；序数；倍数；分数；大数；约数

1. 倍数：三种方式—twice as +adj. + as;

twice more + adj. + than;

twice + the size of

①. twice the size of ours 两倍于

②. twice as large as ours 两倍于

③. twice larger than ours 比…大两倍

④. twice as many people as ...两倍于……的人

2. 序数：

①. one's fifteenthbirthday 十五岁生日

②. a secondtime/birth又一次/再生

the/a firstprize 一等奖

③. the secondlargest city 第二大城市

④. be second(only) to (none) 仅次于/不亚于

⑤. the first/lastto come第一个/最后一个到

3. 复数：“…（数量）的…”三种方式—数+量’s +名词；a 数-量 +名词；a 名词 +数+量+形

①. three days' stay（三天的停留）；

one minute's wait（一分钟的等候）

②. a fifteen-year-old boy（一个十五岁的男孩）

③. a wall two meters high（两米高的墙）

a boy fifteen years old（一个十五岁的男孩）

4. 约数：年代；年龄；大概时间；半个；几十个

①. In the 1980s 在20世纪八十年代

②. in one's fifties 在他五十多岁的时候

③. in the past/recent/last ten years 在过去的…年里

④. in a day or two 一两天后

⑤. half amonth/day 半个月/天

⑥. two days andhalf/two and a half days 两天半

⑦. hundreds of 几百个

⑧. tens of thousands of 成千上万

⑨. hundreds of thousands of 几十万

⑩. dozens(打)/scores(二十)/decades(十年) of

成打的/几十/几十年的

5. 分数：基数-序数（s）

①. one second/twothirds二分之一/三分之二

②. a half/aquarter 一半/四分之一

6. 大数：在可数名词的复数前；在不可数名词前

仅用于可数名词	两者均可	仅用于不可数名词
many	lots of；a lot of	much
a good many	plenty of	a great deal of
a large number of	a large quantity of	a large amount of
quite a few	quantities of	not a little