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': 'All are effects of sympathetic stimulation, EXCEPT \nSelect and explain. \nA. Increased conduction velocity, B. Increased heart rate, C. Increased refractory period, D. Increased contractility of heart', 'role': 'user'}, {'content': 'Answer: C \nExplanation: When sympathetic system is activated, the refractory period is decreased.', 'role': 'assistant'}]