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