Ultrasonic waves; option [B] cannot be heard by humans. These waves have frequencies above 20,000 Hz, which is beyond the upper limit of human auditory perception. While some animals, such as bats and certain rodents, can detect and utilize ultrasonic waves for echolocation and communication, humans require specialized equipment like ultrasound machines to generate and detect these waves.

The inability of humans to hear ultrasonic waves is due to physiological limitations in the human auditory system, which is sensitive to frequencies typically ranging from 20 Hz to 20,000 Hz. Beyond this range, the cochlea in the inner ear cannot detect vibrations as sound. Instead, ultrasonic waves are utilized in various technological applications such as medical imaging, industrial processes, and underwater navigation where their unique properties are advantageous. Thus, the correct answer remains [B] cannot be heard.