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': 'Constant PR inverval is seen in- \nSelect and explain. \nA. First degree block, B. Second degree - Mobiz type I block, C. Second degree - Mobiz type II block, D. Third degree block', 'role': 'user'}, {'content': 'Answer: A \nExplanation: constant PR interval is a feature of first degree hea block second and third degree hea block doesnt have constant intervals Ref Harrison 20th edition pg 1534', 'role': 'assistant'}]