a few adj.一些，几个。
〔辨析〕在数量上用于肯定意义，强调有一些，后接复数可数名词。
〔例证〕I have a few friends in New York.我在纽约有几个朋友。
I have saved a few chocolates for the children.我留了一些巧克力糖给孩子们。
a number of 许多···，若干···。
〔辨析〕强调数量的概念，也可说a large／small number of，后接复数可数名词，谓语动词用复数。
（例证〕There are a number of chairs in the hall.大厅里有一些椅子。
A large number of children survived the earthquake.
不少孩子从地震中幸存了下来。
A small number of students at this college are studying electronics.
这所学院里有少数学生在学电子学。
（小贴士）the number of表示“···的数量（或数目）”，相应的谓语动词要用单数。例如：
The number of students at this college is decreasing.
这所大学的学生人数在减少。
several adj.几个，数个。
（辨析）相对于a few，some 而言较为正式，一般只能用于肯定句，强调“不止一两个”，后接复数可数名词。
（例证）She raises several pigs.她养了好几头猪。
After several visits to Beijing, she had learned a little Chinese.
数次访问北京后，她学会了一点汉语。
There are several holes in the wall.墙上有几个洞。
some adj.一些，若干。
（辨析）带有不确定性，多用于肯定句中，后接复数可数名词或不可数名词。
（例证）Some co-workers attended his party.
些同事参加了他的聚会。
He has been gone for some time.他已经离开一段时间了。
He saved some apples for his children.
他给孩子们留了些苹果。