**Core Concept**
The corrected effective temperature (CET) is a measure of thermal comfort in indoor environments, combining air temperature, humidity, air velocity, and radiant temperature. It reflects how humans perceive thermal comfort in workplaces, particularly in industrial settings.

**Why the Correct Answer is Right**
For optimal comfort and productivity in factories, the corrected effective temperature should be between 69°F and 76°F. This range aligns with human thermoregulatory needs, ensuring sufficient cooling without excessive energy use or risk of heat stress. The World Health Organization and occupational health guidelines recommend this range for indoor work environments to maintain worker comfort and reduce fatigue.

**Why Each Wrong Option is Incorrect**
Option A: Below 69°F may feel too cold, leading to discomfort, shivering, and reduced alertness.
Option C: Temperatures between 77–80°F are already warm and may cause heat strain, especially in poorly ventilated factories.
Option D: 81–82°F is excessively hot and increases risk of heat exhaustion and reduced work performance.

**Clinical Pearl / High-Yield Fact**
In industrial settings, thermal comfort is directly linked to worker productivity and safety—maintaining CET between 69–76°F ensures both comfort and efficient work performance without overcooling or overheating.

✓ Correct Answer: B. Between 69 and 76