a number of作主语,谓语动词用什么形式

a number of 是许多的意思,相当于a lot of.谓语动词用复数.
如：A number of people were injured in the terrible earthquake.
注意若主语是“ the number of+ 名词”时,谓语动词则要用单数形式.例如：
The number of the people invited was fifty, but a number of them were absent for different reasons.