What is the best way to describe a gregorian chant? a) haunting sounds without harmony b) melodic song that included chords c) musical arrangement sung in harmony d) repetitive tune by a single person

The answer is C. Musical arrangement sung in harmony. An arrangement is a musical reconceptualize of a previously collected work. It may contrast from the original work by means of reharmonization, melodic paraphrasing, orchestration, or elaboration of the formal structure.