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': 'Cataract brunescens results due to deposition of - \nSelect and explain. \nA. Copper, B. Iron, C. Silver, D. Urochrome', 'role': 'user'}, {'content': 'Answer: D \nExplanation: In nuclear senile cataract, there may or may not be associated with deposition of pigment urochrome and/or melanin derived from amino acids in the lens.\nCommonly observed pigmented nuclear cataracts are amber, brown (cataract brunescens) or black (cataract nigra) and rarely reddish(cataract Rubra) in colour.', 'role': 'assistant'}]