1)不定冠词a/an表示任何一个，只能用于单数可数名词前，不用于不可数名词前。

　　【例如】

　　We are going to have a committee meeting this afternoon.There will be discussion and argument at the meeting.

　　2)表示职业、宗教、民族和年龄的名词作表语，前面一般加a/an。

　　【例如】

　　He is a lawyer, a bachelor and a Christian.3) a用于下列固定词组：a lot of, a great many of(加可数名数复数),a great deal of(加不可数名词), a large amount of, a number of, a couple, a dozen, a hundred.