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: Unknown
[{'content': 'SI unit of brightness of a point light source is? \nSelect and explain. \nA. Candela, B. Lumen, C. Lux, D. Lambert', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]