Which areas are prohibited from being used as return air sources?

The choice that identifies the areas prohibited from being used as return air sources is accurate because it focuses on spaces that typically contain contaminants or may have fluctuating temperatures and humidity levels that can adversely affect indoor air quality.

Bathrooms, for instance, are often high in humidity and may contain mold and bacteria that, if circulated through the HVAC system, can lead to health concerns and deterioration of air quality. Kitchen areas are similarly prohibited because they can accumulate cooking odors, grease, and particulate matter, all of which are undesirable in the return air. Toilet rooms and closets also qualify as unsuitable return air sources, as they may harbor unpleasant odors or other pollutants, creating similar issues for air quality and HVAC efficiency.

In contrast, other answer choices may include rooms where the air quality is less compromised and thus may be acceptable for return air sources according to the guidelines established in the International Mechanical Code. It is essential to recognize that the intent behind these prohibitions is to maintain a healthy and comfortable indoor environment by avoiding the circulation of potentially harmful air.