**Core Concept**
Whispering is a soft spoken voice, typically used in quiet environments or to avoid being overheard. The intensity of sound produced by whispering is measured in decibels (dB) on the sound level meter.

**Why the Correct Answer is Right**
The sound intensity of whispering is usually in the range of 20-30 dB. This is because whispering involves the production of sound through the movement of air through the vocal cords, but with minimal vibration and noise. The low sound intensity of whispering is necessary to avoid disturbing others and to maintain a quiet atmosphere. The range of 20-30 dB is considered a very soft sound, barely audible to the human ear.

**Why Each Wrong Option is Incorrect**
**Option B:** 30-40 dB is too high for whispering, as it would be more akin to a normal conversation or a soft spoken voice.
**Option C:** 40-50 dB is even louder, equivalent to a moderate conversation or a radio at a low volume.
**Option D:** 50-60 dB is a relatively loud sound, comparable to a vacuum cleaner or a normal conversation in a quiet room.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that sound levels above 85 dB can cause hearing damage, and prolonged exposure to sounds above 50 dB can lead to noise-induced hearing loss.

**✓ Correct Answer: A. 20-30db**