Final answer:
Steve Reich's Electric Counterpoint, III is defined by short, repeated melodic ideas and regular rhythms with varying patterns, but it does not contain irregular rhythms with unchanging patterns or one long, lyrical melody.
Step-by-step explanation:
Reich's Electric Counterpoint, III is a piece of music that is characteristic of Steve Reich's minimalist style. One of the defining features of this composition is the use of short, repeated melodic ideas (ostinatos) which layer upon each other to create a complex tapestry of sound. Additionally, Reich employs regular rhythms with varying rhythmic patterns to create both a sense of stability and interest.
However, irregular rhythms with unchanging rhythmic patterns do not describe this piece, as Reich's rhythms, while complex, are often quite regular. Furthermore, the piece does not contain one long, lyrical melody; instead, it relies on the interaction of brief repetitive motifs.