The properties of ultrasound that make it useful, are

Options

A. high power and high speed
B. high power and good directivity
C. high frequency and high speed
D. high frequency and bending around the objects.

Explanation

**Step-by-Step Solution:**

1. **Understanding Ultrasound:**
- Ultrasound refers to sound waves with frequencies higher than the upper audible limit of human hearing, typically above 20 kHz. It has various applications in medical imaging, therapy, and industrial testing.

2. **Property 1: High Power**
- One of the key properties of ultrasound is its high power. This characteristic allows ultrasound to be used effectively in medical treatments, such as breaking up stony deposits in the human body, like kidney stones.
- **Application:** High power ultrasound can break up stony deposits or tissues, assisting in medical procedures to eliminate stones from the kidneys.

3. **Property 2: Good Directivity**
- Another important property of ultrasound is its good directivity. This means that ultrasound waves can be directed precisely to a specific area.
- **Mechanism:** This is achieved by modulating audible sound into high-frequency ultrasound. The higher frequency sound waves have shorter wavelengths, which allows them to be focused more effectively than lower frequency sounds.
- **Application:** Good directivity enables ultrasound to accelerate the effect of drugs in targeted areas, measure the elastic properties of tissues, and conduct research on small particles.

4. **Conclusion:**
- The combination of high power and good directivity makes ultrasound a valuable tool in various fields, particularly in medicine for diagnostics and treatment.