题目内容：

The number of people invited was fifty,but a number of them were absent for different reasons.
the number of和a number of

优质解答

被邀请的人数是50,但他们中的一些人由于不同原因缺席了.
the number of ...的个数
a number of 一些
上面的,你们搞得也太复杂了吧