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: Biochemistry
[{'content': 'Keratin in skin is softer than keratin in nail because keratin in skin has - \nSelect and explain. \nA. Less number of disulphide bonds, B. Less number of salt bridges, C. High sodium content, D. Different affinity for water', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The extent of keratin hardness depends on the number of disulfide bonds/sulfur content. The more the number of disulfate bonds, the harder the keratin is.\nKeratin in skin is softer than keratin in nails because it has less number of disulfide bonds.', 'role': 'assistant'}]