This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: School Health, Geriatrics, Subject name: Social & Preventive Medicine
Recommended doors + windows area (% of floor area) in a school class must be: 
Select and explain. 
A. 10%, B. 15%, C. 20%, D. 25%
D: 25%
Answer: D: 25% 
Explanation: Healthful school environment: Minimum recommended standards:- 1 classroom- <40 students Doors and window: Doors and window area > 25% of floor area Per capita space > 10 sq. feet Desk- minus type Natural light from left side 1 urinal per 60 students 1 sanitary latrine per 100 students.