基数词在用来表示准确数字的情况下不能加复数后缀"s"。以下基数词可以加复数后缀"s",因为它们表达的都是大概的数字。

1.thousands of / millions of / hundreds and hundreds of / hundreds of thousands of / thousands upon thousands of 成千上万……

例:There are hundreds of thousands of people in the park. 公园里的人有千百个。

2. in twos and threes 三三两两

例:They came home from church by twos and threes. 他们三三两两地从教堂回来。

3. at sixes and sevens 乱七八糟

例:His wife was away and the house was at sixes and sevens. 他妻子不在,家里乱七八糟的。

4. in one's fifties 在五十多岁时(fifties 前可插入 early, late, mid-, middle)

例:The boys are all in their teens. 那些男孩年纪都在十几岁。

Jane is only in her early forties. 简才刚刚四十出头。

She was in her mid-twenties. 她有二十五、六岁。

He was then in his late seventies. 他当时已经快八十岁了。

5. in the 1960s (in the 1960's) 二十世纪六十年代

例:He made acquaintance of her in the 1960s. 六十年代他认识了她。