The original sentences have a subject-verb agreement error because the plural subject 'horses' does not match the singular verb 'gallops.' To correct this, we should change 'gallops' to 'gallop.' This change ensures that both the subject and verb agree in number. ;
The best option to correct the subject-verb agreement error in the sentences is to change "gallops" to "gallop," ensuring the plural subject "horses" matches the verb. This adjustment aligns the number of the subject and verb, resolving the inconsistency. Therefore, the chosen answer is option D.
;