Final answer:
In music theory, repeating phrases builds structures that create dynamics and motion, providing rhythm and emotional texture.
Step-by-step explanation:
The answer to the student's question is D) Phrases. In music theory and composition, once you start repeating phrases, structures start to form, creating dynamics and motion. A phrase in music is a unit of musical meter that has a complete musical sense of its own, built from smaller units known as motifs. Much like in language where phrases are components of sentences, in music, phrases are part of a larger whole. Repetition is key in music; it provides structure and helps to establish motifs and themes. It can also lead to the development of rhythm and melodicism within a piece, contributing to the overall texture and emotional feel of the music.