This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiovascular system, Subject name: Physiology
[{'content': 'Vagal stimulation in hea decreases hea rate by \nSelect and explain. \nA. Decrease in action potential spike, B. Decrease in slope of prepotential, C. Increase in repolarisation, D. Decrease in conduction', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]