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: Physiology
[{'content': 'Parasympathetic stimulation of heart causes: \nSelect and explain. \nA. SA node decreases firing, B. Increased AV node excitability, C. Decreased ventricular contraction, D. Tachycardia', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]