Persichetti Exercise 4 - 40 for String Quartet

I've now moved on to Chapter 4 of Persichetti's "20th Century Harmony" which is about quartal chords.  The prompt for this one was "10.  Extend the following string-quartet opening.  Feature pentatonic melodic and quartal harmonic writing."

Thanks for listening and I'd appreciate any comments, suggestions, critiques or just observations!

Very modern sounding, and I can definitely hear the influence of the pentatonic scale. The harmony makes this scale not sound so sing songy.  Nice use of key changing, and after the musical phrase I like how you descend down the scale (such as around 0:36 and 0:39).