Which sentence is a run-on sentence? A. The cheetah is the fastest land animal; the sailfish is the fastest animal in water. B. A professional marathon runner can run 26 miles in just over two hours. C. The gazelle can only run about half as fast as the cheetah. D. Snails move very slowly, a banana slug can move 6 inches in two hours.

The run on sentence is D. Snails move very slowly, a banana slug can move 6 inches in two hours.

A run-on sentence is a sentence that has at least two independent clauses which are not properly punctuated.

When two independent clauses are connected only by a comma, it is a run-on sentence that is called a comma-splice.

Run-on sentences can be corrected with the use of conjunctions (for, and, nor, but, or, yet, so)

Snails move very slowly, and a banana slug can move 6 inches in two hours. (corrected run-on sentence)

The answer is D. Snails move very slowly, a banana slug can move 6 inches in two hours