the number of /a number of
这两个词组不同之处,就在于其前的冠词上.
1）the number of…表示“……的数量”.作主语的中心词时,谓语动词用单数形式,后常跟large,small等词作表语.如：
The number of the students is very large in our school.我们学校的学生数量非常大.
The number of the students in our school is2000.我校的学生人数是两千.
2）a number of表示“若干的；；许多的”.起修饰作用,相当于many或a lot of,number前可以加small,large词来表示程度.A number of+复数可数名词作主语时,其谓语动词用复数形式.如：
A number of the students are playing football.许多学生在踢足球.