In jazz, what is the term for a short progression of chords that can be repeated indefinitely?

Name the term for a piece of standing scenery used as a background or to simulate the walls of a room

a. sets b. flats c. props d. platforms

A/an _____________ is a half arch used to counteract the outward thrust of the vault and to transfer the thrust to piers outside the walls.

A. aqueduct B. flying buttress C. crusade D. troubadour