Answer: B
To measure a lower-pitched sound wave, you would measure fewer compressions per second. Pitch relates to frequency by measuring how many times a second the particles vibrate. Therefore, the lower-pitched sounds, the fewer compression waves or sound waves are produce because low-frequency sounds have greater distance between each wave.
Moreover, the frequency of a wave is measured as the number of complete back-and-forth vibrations of a particle of the medium per unit of time. The universal unit for frequency used is the Hertz (abbreviated Hz), where 1 Hertz = 1 vibration/second.