1. The sound level in decibels is related to intensity by

2. If the sound absorber attenuates the sound level by $20\,\text{dB}$, then the decrease in level is

3. Using the decibel relation for two intensities $I_1$ and $I_2$:

Since the level decreases by $20\,\text{dB}$,

4. Divide by 10:

5. Taking antilog:

So the intensity decreases by a factor of $100$.

6. Checking options:

• A: $100$ ✅
• B: $1000$ ❌
• C: $10000$ ❌
• D: $10$ ❌

Therefore, the correct answer is A.