Conventions of Composition Rule 137

Rules: If you use plurals in the beginning of a sentence, any words connected to those plurals must also take a plural form. Same for singular.

Examples:

Wrong: People talk about their life in interesting ways.

Correct: People talk about their lives in interesting ways.

Practice fixing errors in agreement:

1. I looked at the cars in the lot and noticed their color.
2. At two years old, Charlie could identify triangles, circles, squares; he knew objects' shape well.

Resources for further explanation about all kinds of agreement errors:

Wikipedia's Agreement