Final answer:
The recommended relative humidity in a building for health reasons is 30-70%. This range helps in reducing health risks and protecting the building's interior and contents.
Step-by-step explanation:
From a health standpoint, the recommended relative humidity desirable in a building is B) 30-70%. This range of relative humidity is considered comfortable for human beings and can help in reducing the risk of respiratory infections and allergies. Maintaining this level of humidity can also prevent the growth of mold, bacteria, and viruses which thrive in environments with high humidity. Moreover, it can protect furnishings and electronic equipment from the damaging effects of too low or too high humidity levels.