This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Fluid & Electrolyte, Subject name: Medicine
[{'content': "Tall 'T' waves are seen in: (Repeat) \nSelect and explain. \nA. Hyperkalemia, B. Hypocalcemia, C. Hypercalcemia, D. Hypokalemia", 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans: A (Hyperkalemia) Ref: Harrison 's Principles of Internal Medicine, 18ed.Explanation:ECG changes in HyperkalaemiaTall T waves (Earliest sign)Prolonged PR intervalWidened QRS intervalFlattened P wavesArrythmias including bradycardia, ventricular tachycardia or fibrillationSinus arrest or nodal rhythm with possible asystoleECG changes in HypokalaemiaFlattened T wavesST segment depressionProlonged QT intervalTall U wavesAtrial arrythmiasVentricular tachycardia or ventricular fibrillation", 'role': 'assistant'}]