Question 1: This is somewhat reminiscent of the early modern ocean
sounding unit "mark" (a synonym for ________), which was also unit-first, and may have
influenced the use of the term Mach.

Question 2: Because the Mach number is often viewed as a ________ rather
than a unit of measure, with Mach, the number comes after
the unit; the second Mach number is "Mach 2" instead of "2 Mach"
(or Machs).

Question 3: Assuming air to be an ________, the formula to compute Mach number
in a subsonic compressible flow is derived from Bernoulli's equation for
M<1:^{[3]}