This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Eczema and related disorders, Subject name: Dental
[{'content': 'Commonest metal causing skin hypersensitivity? \nSelect and explain. \nA. Brass, B. Copper, C. Iron, D. Nickel', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Metal dermatitis is most frequently caused by nickel, chromates and mercury. Nickel is naturally present in food (green leafy vegetables) and also present in jewellery, household equipment, wearing apparel and industry.', 'role': 'assistant'}]