Which of the following is an example of a run-on sentence?

1. she likes her cereal with no milk at all.
2. i like my cereal with lots of milk.
3.most people eat cereal, it’s healthy.
4. when they eat it, they use milk.

3. Most people eat cereal, it's healthy is an example of a run-on sentence.

Explanation:

Run-on sentences occur when two or more independent clauses are not connected properly. A common type of run-on sentence is the one resulting from a comma splice, where the author failed to use a transitional expression and used just a comma to join two independent clauses -a clause that contains a subject and a predicate and can stand alone as a sentence. This is the case of sentence 3.

an expression designed to call something to mind without mentioning it explicitly; an indirect or passing reference.