The shoppers in the store look tired.
[Who looks tired? The subject, shoppers, is plural.]
Her collection of baseball cards is valuable.
[What is valuable? The subject, collection, is singular.]
The government's proposals about preserving the environment cause controversy.
[What things cause controversy? The subject, proposals, is plural.]
|Example||His assistant always makes mistakes.|
|Example||His daughter, as well as his two sons, wants him to move.|