1.基数词是表示数目的数字，如：

one(一), two(二), ten(十), twenty(二十), one hundred(一百), two thousand(两千), ten million(一千万), three billion(三十亿)等。

2.基数词可相当于名词，可有复数形式,这时它所表达的数量不很准确,仅仅是一个大概范围。hundred, thousand和million等的复数形式之后常接of片语，表示数以百计、千计、百万计等;of片语有时也可省略。

I have found a way to make thousands of dollars.

我已经找到一个赚成千上万美元的方法。

They arrived in twos and threes.

他们三三两两的来了。

Hundreds of lives were lost in the fire.

数百人在大火中丧生。

Thousands and thousands of people got infected with flu every year.

每年成千上万的人受到流行性感冒感染。

In order to maintain its operation, the company needs millions of dollars.

这个公司需要数百万美元以维持其运作。

3.dozen, score, hundred, thousand, billion, million之前有确定的数字时不论后面有无of，字尾都不加s。

It is two thousand of quarters, 250 dollars.

是两千个25美分，250美元。

4.基数词表示几十的复数数词的变化形式与名词相同，一般用来表示人的不确切年龄。

I will become a famous painter in my twenties.

我将在二十岁时成为知名画家。

He died in his early thirties.

他三十刚过就死了。

5.基数词在句中可作主语、宾语、修饰语、主语补语和同位语。

Thirteen is an unpropitious number.

13是个不吉利的数字。

Seven is an odd number.

七是奇数。

基数词Seven作主语。

I still need two.

我还需要两个。

I need at least eight.

我至少需要八个。

基数词eight作宾语。

Return those two coins to me!

把那两枚硬币还给我!

Thirty students are doing chemical experiments in this classroom.

三十个学生在这间教室里做化学试验。

基数词Thirty作修饰语。

Six plus two is eight.

六加二是八。

Four plus two is six.

四加二是六。

基数词six作主语补语。

Have you ever seen us two?

你见过我们两个人吗?

基数词two作宾语us的同位语。