1、只能修饰可数名词的：a large/ great/ good number of, a good/ great many, dozens of, scores of, quite a few。

2、只能修饰不可数名词的：a great deal of, a large amount of, quite a little,a large sum of。

3、既可修饰可数也可修饰不可数名词的：plenty of, a lot of, lots of, a large quantity of, a good supply of。

4、但是a number of不能修饰不可数名词。