The speed of highly penetrating ultrasonic waves is:

Human ears are capable of hearing sounds with a frequency range of $20Hz$ to $20kHz$. Infrasonic noises are those with frequencies less than $20Hz$, and ultrasonic sounds are those with frequencies greater than $20kHz$.
The frequency of a wave is the number of times per second that the wave oscillates about its mean location. It is equivalent to the wave's period's reciprocal.
The distance a wave travels in a single instant is known as its wavelength. It may also be described as the separation between two wave crests or troughs.
Only a restricted range of sound wave frequencies may be detected by human ears.

A person's hearing range is $20Hz$ to $20kHz$, and their wavelength range is $1.72 cm$ to $17.2 m.$
Infrasonic noises are those with frequencies lower than$20Hz$, and ultrasonic sounds are those with frequencies higher than $20kHz$. The intense ultrasonic vibrations have a frequency of up to ${10}^{7}Hz$ is much over the human hearing threshold and is thus not audible to humans.
Since the speed of extremely penetrating ultrasonic waves is substantially higher than that of audible sound waves.

Hence, the correct answer is option C.