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': 'Constant PR inverval is seen in -a) First degree blockb) Second degree - Mobiz type I block.c) Second degree - Mobiz type II blockd) Third degree block \nSelect and explain. \nA. a, B. bc, C. ac, D. b', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]