The frequency of ultrasound is :

Options

A. Above 20000 vibration/sec
B. Under 20000 vibration/sec
C. Under 20 vibration/sec
D. None of the above

Explanation

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks for the frequency range of ultrasound. We need to identify the correct frequency range from the given options.

2. **Defining Ultrasound**: Ultrasound refers to sound waves that have a frequency above the human audible range. The human ear can typically hear sounds in the frequency range of 20 Hz to 20,000 Hz (20 kHz).

3. **Identifying the Frequency Range**:
- Frequencies above 20,000 vibrations per second (20 kHz) are classified as ultrasound.
- Frequencies below 20 Hz are classified as infrasound.

4. **Analyzing the Options**:
- The options provided are:
- Above 20,000 vibrations per second
- Under 20,000 vibrations per second
- Under 20 vibrations per second
- None
- Based on our definition, the correct answer must be "above 20,000 vibrations per second".

5. **Conclusion**: Therefore, the frequency of ultrasound is above 20,000 vibrations per second.

### Final Answer:
The frequency of ultrasound is above 20,000 vibrations per second.

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