—Class is over.—Look number of students are playing football there. Let’s go and join t

问题补充：

—Class is over.

—Look, number of students are playing football there. Let’s go and join them.

A. /

B. a

C. an

D. the

答案：

A. /

(答案→)B. a

C. an

D. the

解析：句意：--下课了。--看，有许多的学生正在那踢足球。让我们去加入他们吧。a number of是大量的，等于a lot of后面接名词复数。the number of是……的数量，后面接名词复数，例如:A number of apples are red许多苹果是红色的。The number of students is 2000学生的数量是2000人。a number of…… 许多……或者很多……,谓语动词要用复数e.g. A number of students are playing.很多学生在玩。the number of……的数量 谓语动词要用单数e.g. The number of the students is 50.学生的数量是50。故选B