Why would a scientist have difficulty using sound waves to measure the thickness of a very wide, solid rock mountain?

Since the sounds are travelling at about the same speed, the one with the shorter wavelength "waves" more frequently; it has a higher frequency, or pitch. ... The shorter the wavelength, the higher the frequency, and the higher the pitch, of the sound. In other words, short waves sound high; long waves sound low.

the answer is c.) there is a warm front in region a and a stationary front in region b.