This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: ECG and Arrhythmia 2, Subject name: Medicine
[{'content': 'A 30-year-old man presents with recurrent attacks of feeling dizzy. ECG was done. What is the diagnosis? \nSelect and explain. \nA. Atrial fibrillation, B. PSVT, C. Mobitz I hea block, D. Complete hea block', 'role': 'user'}, {'content': 'Answer: C \nExplanation: HR is regularly irregular due to change in rhythm. Axis is normal. Progressive lengthening of PR interval followed by dropped beat is seen. PR interval before the dropped beat is more than PR interval in subsequent beats. Dx: Mobitz I hea block.', 'role': 'assistant'}]