This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
[{'content': "Canon 'a' waves in JVP represents: March 2007 \nSelect and explain. \nA. Complete hea block, B. 1st degree A-V block, C. Sinus bradycardia, D. Tachycardia", 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. A: Complete hea block', 'role': 'assistant'}]