This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Environment and health, Subject name: Social & Preventive Medicine
[{'content': 'Sling psychrometer is used for measuring - \nSelect and explain. \nA. Air velocity, B. Rain fall, C. Median radiant temperature, D. Relative humudity', 'role': 'user'}, {'content': "Answer: D \nExplanation: Relative humidity of air may be obtained from the readings of sling psychrometer /whirling psychrometer. Park's Textbook of Preventive and Social Medicine, 25th Edition, Pg 809", 'role': 'assistant'}]