This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Fluids and Electrolyte Imbalance, Subject name: Medicine
[{'content': 'Most common cause of hypernatremia? \nSelect and explain. \nA. Primary hypodipsia, B. Carcinoid syndrome, C. Renal losses, D. Sweating', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Elderly individuals with reduced thirst and/or diminished access to fluids are at the highest risk of developing hypernatremia. Patients with hypernatremia may rarely have a central defect in hypothalamic osmoreceptor function, with a mixture of both decreased thirst and reduced AVP secretion', 'role': 'assistant'}]