What genre of music is a small-scale work, portraying a single mood, emotion, or idea?

The traditional definition of music is

A) something that sounds pleasing to the ear B) anything with a beat C) that which can be traced back to the ancient culture of the Greeks D) the organization of sound in time E) non-existent; music cannot be defined

Each successive variation in a theme with variations ________.

A. is usually in the same key B. is usually in a new key C. retains some elements of the theme D. presents a new melodic idea