Answer:
The correct statement is option D, that is, neither ultrasonic nor infrasonic vibrations can be heard by humans.
Step-by-step explanation:
The ultrasonic vibrations are the sound waves exhibiting the frequency of more than 20000 Hz, whereas the upper-frequency limit in human beings is about 20 Hz. Humans cannot hear the ultrasound as it is more than 20 Hz.
On the other hand, the infrasonic vibrations refer to a low-frequency sound, it is lower in frequency in comparison to 20 Hz, that is, the usual limit of human hearing. Thus, for humans to perceive infrasound, the pressure of the sound must be adequately high.