A. The ratio of the speed of the aircraft to the speed of sound in the surrounding air
B. The altitude of the aircraft
C. The pressure difference between the top and bottom of the wing
D. The ratio of the aircraft's weight to its lift
Explanation:
Mach number is the ratio of the speed of the aircraft to the speed of sound in the surrounding air, indicating whether the aircraft is subsonic, transonic, supersonic, or hypersonic.