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: Pharmacology
[{'content': 'Vagal stimulation of heart causes ? \nSelect and explain. \nA. Increased heart rate, B. Increased RR interval in ECG, C. Increased cardiac output, D. Increased force of contraction', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]