Which of these sounds is harmful to human beings ?

Options

A. Aircraft take off
B. Normal speech
C. Chirping of birds
D. Rustling of leaves

Answer

### Step-by-Step Solution:

1. **Understanding Harmful Sounds**:
- To determine which sounds are harmful to human beings, we first need to understand what makes a sound harmful. Harmful sounds are typically those that have a very high loudness.

2. **Loudness Measurement**:
- Loudness is measured in decibels (dB). Sounds that exceed a certain threshold can cause damage to our hearing.

3. **Threshold of Harmfulness**:
- Generally, sounds above 100 dB are considered harmful. Sounds reaching 120 dB or higher can be particularly dangerous and should be avoided.

4. **Examples of Sound Levels**:
- Normal conversation typically occurs at around 60 dB, which is safe for human hearing.
- The chirping of birds is around 40-50 dB, and rustling of leaves is even lower, around 20-30 dB. Both of these sounds are not harmful.

5. **Identifying Harmful Sounds**:
- An example of a harmful sound is the noise produced when an aircraft takes off, which can exceed 150 dB. This level of sound is harmful and can cause hearing damage.

6. **Conclusion**:
- Based on the information, the sound that is harmful to human beings is the sound of an aircraft taking off, as it exceeds the safe threshold of 100 dB.