How do you develop a good characterization in improvisation?

Artists best achieve contrast in a composition by: a. drawing with realism b. shading a drawing with dark and light values c. using drawing techniques like stippling and hatching d. focusing on line and shape in a drawing

Nstrumental music that supports the main part(s) chamber music 2. a large group of instruments usually including woodwinds, brass, and percussion band 3. music written for small ensembles for an intimate setting accompaniment 4. a person who leads an ensemble conductor 5. an electronic keyboard capable of multiple instrument sounds

In a paragraph of no less than 125 words, explain the single most important factor involved in advancing american classical music in the twentieth century.