Mach number is significant in_____________________?

A. supersonics, as with projectiles and jet propulsion
B. full immersion or completely enclosed flow, as with pipes, aircraft wings, nozzles etc.
C. simultaneous motion through two fluids where there is a surface of dis-continuity, gravity force, and wave making effects, as with ship’s hulls
D. all of fhe above
E. none of the above