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
Psychrometer is used to measure - 
Select and explain. 
A. Humidity, B. Air velocity, C. Room temperature, D. Radiant temperature
A: Humidity
Answer: A: Humidity 
Explanation: Psychrometer is a device to measure humidity of air. Sling psychrometer consist of 2 mercury tgermometer mounted side by side on.suitable wooden frame with handle for rotating the instrument.Underlying principle is that by roatating the bulbs are exposed to air at a definite velocity. By using suitable tables the relative humidity of air can be obtained from readings of psychrometer. Assman psychrometer is apoable instrument to measure humidity. Parks textbook of preventive and social medicine.K Park. Edition 23.page no:749.