a number of the number of

a number of 是指“大量的”,后面的动词是复数形式
e.g.
A number of our classmates love English.
A number of studends are playing.许多学生在玩耍.
这里的a number of = a lot of =many .修饰可数名词.
the number of 是指“.的数量”,后面的动词是单数形式
e.g.
The number of our classmates is 45.
The number of students in my class is 56.我的班级的学生数是56.
这里的the number of 表示数目.后面的be动词一般为单数.is/was