All of the following are musical elements of Duke Ellington’s late 1920s and early 1930s "breakthrough" except:______.
A. He clarified the nature of big-band jazz.
B. He elevated jazz as a dignified, intellectual music.
C. He composed popular songs in individual and adventurous ways.
D. He made stride piano a part of his piano and orchestral style.
E. He focused solely on blues style.