Final answer:
Christoph Willibald Gluck is the noted reformer of eighteenth-century opera, focusing on dramatic effect and simplicity, unifying aria and recitative. Option C is correct
Step-by-step explanation:
The reformer of eighteenth-century opera noted among the options provided is C. Christoph Willibald Gluck. Gluck sought to reform the opera by focusing on simplicity and dramatic effect rather than the elaborate ornamentation and virtuosic aspects that characterized much of the operatic music of that time.
His work aimed to make the music serve the poetry by emphasizing the dramatic intent of the text and unifying aria and recitative, which helped to transform opera into a more cohesive art form.