Final answer:
The correct option to correct the run-on sentence in the student's essay about horses is Option A, which breaks the initial run-on into two separate sentences, enhancing structure and clarity.
Step-by-step explanation:
The question relates to correcting a run-on sentence found in a student's essay about horses. A run-on sentence is an incorrect sentence in which two or more independent clauses are incorrectly joined without proper punctuation or conjunction.
The correct revision that avoids a run-on sentence is Option A: Horses have excellent hearing. They have eight muscles in their ears and can turn their ears nearly 180 degrees to hear what is happening around them.
This option breaks the run-on sentence into two separate sentences connected by a conjunction, which improves the sentence structure and clarity. The essay excerpt suggests knowledge of mammalian biology, discussing how horses have superior hearing due to specific anatomical adaptations, which is interesting considering the general themes of hearing and balance as related to mammals and their activities like riding or experiencing music.