a number of後面接複數還是單數

The new management intends to institute a number of changes.

新任管理層打算實行一些改革。

There are a number of different points of view on this issue.

在這個問題上意見紛紜。

I have a number of things to do today.

我今天有許多事情要做。

A number of measures were taken to alleviate the problem.

採取了一系列措施緩解這個問題。

A number of social factors influence life expectancy.

諸多社會因素左右着人的預期壽命。