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': 'Which of the following regions has the lowestatmospheric humidity? \nSelect and explain. \nA. Equatorial, B. Monsoon, C. Prairies, D. Polar', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Humidity or moisture is always present in the atmosphere. The amount of moisture which air can hold depends upon its temperature. If air is cooled excessive moisture precipitates for a paicular temperature. This is called the dew point.', 'role': 'assistant'}]