what are the  two properties of ultrasound that make it useful to us?

Define the vibration's frequency and amplitude. Identify the various vibrational kinds based on their frequency range. More than 20000 Hz is the frequency of the ultrasound. Learn how to employ various vibrational kinds based on their qualities as a result of their frequencies and wavelengths.
A phenomenon known as vibration is when an item oscillates about its equilibrium position. The vibration may be regular, like that of a pendulum swinging, or it may be erratic.
When a vibrating item causes the medium it is in contact with to vibrate, a sound wave is created.
The greatest distance an item may travel on either side of its equilibrium position can be used to measure the amplitude of vibration.

The amount of vibrations that take place per second determines a vibration's frequency. It may be explained as the motion of a vibrating item. When an item goes from one extreme position to the other and then returns to the initial extreme position, a full vibration happens. The vibration's frequency is defined as the number of full cycles that take place in a second. Frequency is measured in Hz (hertz). One whole cycle per second is equivalent to one hertz.
Today, ultrasonography refers to sound waves with a frequency greater than 20000 Hz.
Ultrasound has a relatively short wavelength and a high frequency. Ultrasound has a very high energy because of its high frequency.

The route that the ultrasound can take is clearly specified as being straight. Its short wavelength prevents it from bending much near the borders of an obstruction.
Ultrasound applications:
The depth of the view is measured with sonar using ultrasound. In order to detect the reflected ultrasound, the sonar first emits an ultrasonic that is reflected at the ocean's bottom. We can determine the depth of the sea by measuring the time interval.
Crystals and metals may be examined using ultrasound to check for flaws. If there is a flaw or impurity in the material when we transmit ultrasound, the ultrasound will deflect and we will receive a returning signal.

Hence, the correct answer is option A and C.