Which of the following statements is an accurate description of vibrations?

A. The frequency of infrasonic vibrations is much too high to be heard by humans.
B. Neither ultrasonic nor infrasonic vibrations can be heard by humans.
C. Infrasonic vibrations are used in sonar equipment as well as to detect flaws in steel castings.
D. Ultrasonic vibrations have a frequency lower than the range for normal hearing.