This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Social & Preventive Medicine
Sling psychrometer is used for measuring ? 
Select and explain. 
A. Air velocity, B. Rain fall, C. Median radiant temperature, D. Relative humidity
D: Relative humidity
Answer: D: Relative humidity 
Explanation: Ans. is 'd' i.e.. Relative humidity