Question

ultrasound is:
select one:
used to make internal images of the human body.
the speed at which the latest, top - secret jet aircraft fly.
of lower frequency than the human ear can detect.
extremely painful to the human ear.

destructive interference occurs because:
select one:
multiple waves combine to make a wave of smaller amplitude.
waves bend around or through holes in an obstacle.
waves are absorbed and disappear.
two waves add up to make a wave of larger amplitude.

Explanation:

Ultrasound is a type of sound wave with a frequency higher than what the human ear can detect. In medical applications, it is used to create internal images of the human body. For destructive interference, according to the principle of wave interference, when multiple waves combine in a way that their amplitudes subtract (due to a phase difference of \(180^{\circ}\) for example), the resulting wave has a smaller amplitude. This is the definition of destructive interference.

Answer:

For the first question: used to make internal images of the human body.
For the second question: multiple waves combine to make a wave of smaller amplitude.