This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.V.S., Subject name: Medicine
[{'content': 'Giant a waves in JVP is seen in: \nSelect and explain. \nA. Tachycardia, B. Atrial ectopic, C. 1st degree heart block, D. Complete heart block', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Ans: dRef: Harrison, 16thed, p. 1306', 'role': 'assistant'}]