Which is a run-on sentence?
a. roses have sharp thorns, but they are beautiful just the same.
b. acorns drop from oak trees, and they are a food source for squirrels. c. sunflowers are usually yellow, yet some are red or orange.
d. african violets usually have purple flowers some have white ones.

A run on sentence is a sentence that runs on without pause that needs a pause, genes it being called run on. When reading English , the comma shows a pause in the sentence and allows a natural flow. From choices A - C the sentences have flow and include a pause due to the comma. Choice D does not include a comma and when read aloud it sounds rushed and "run on." If it were to be corrected, answer choice D would have a comma placed after the word "flowers".

You answer is d. A run on sentence has no comma. You can also look up on google to give you some examples of run on sentences.