**Core Concept**
Normal conversation sound levels are typically measured in decibels (dB) and can vary depending on the context. In a quiet room, a normal conversation between two people at a distance of 1 meter is considered a moderate sound level.

**Why the Correct Answer is Right**
The sound level of normal conversation at 1 meter distance is approximately 60 dB. This is because the intensity of sound decreases with distance, following the inverse square law. The sound level of a conversation can range from 50 dB to 70 dB, with 60 dB being a typical average value. This value is measured using a sound level meter, which takes into account the frequency and intensity of the sound waves.

**Why Each Wrong Option is Incorrect**
**Option B:** 80 dB is typically the sound level of a vacuum cleaner or a busy street, which is much louder than a normal conversation.
**Option C:** 90 dB is the sound level of a lawnmower or a rock concert, which is extremely loud and would be uncomfortable to listen to for extended periods.
**Option D:** 120 dB is the sound level of a jet taking off or a shotgun blast, which is extremely loud and can cause permanent hearing damage.

**Clinical Pearl / High-Yield Fact**
It's essential to note that sound levels above 85 dB can cause hearing damage over time, so it's crucial to protect one's hearing in loud environments.

**✓ Correct Answer: A. 60 dB**