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: Ophthalmology
[{'content': 'The lens contains the oldest cells in – \nSelect and explain. \nA. Nucleus, B. Anterior surface of lens, C. Posterior surface of lens, D. Nucleo–cortical junction', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The nucleus is the central part containing older fibres. Embryonic zone of the nucleus (embryonic nucleus) contains oldest fibres.\nThe cortex contains the youngest fibres.', 'role': 'assistant'}]