What category of Ellington's work does this piece fit into?

What is a cantus firmus? a. A canon that endlessly circles back to the beginning. b. The highest vocal part in a polyphonic composition; later known as thesoprano part

c. A musical technique in which two or three voices engage in voice exchange. d. A well-established, previously existing melody, be it sacred chant or secularsong, that provides a structural framework for a polyphonic composition.

Swing dominated American popular music

a. during the 1930s b. from about 1925 to 1945 c. from about 1935 to 1950 d. from roughly 1935 to 1945