This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nervous System, Subject name: Physiology
[{'content': 'Colour vision is by: \nSelect and explain. \nA. Rods, B. Cones, C. Occipital cortex, D. Bipolar cells', 'role': 'user'}, {'content': 'Answer: B \nExplanation: B', 'role': 'assistant'}]