This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of protein and amino acid, Subject name: Biochemistry
[{'content': 'Cystine is formed from \nSelect and explain. \nA. Arginine, B. Histidine, C. Cysteine, D. Alanine', 'role': 'user'}, {'content': 'Answer: C \nExplanation: The difference in structure of cysteine and cystine. Two molecules of cysteine are joined together by S--S bond to form one molecule of cystine.Ref: M.N. Chatterjea - Textbook of Biochemistry, 8th edition, page no: 504', 'role': 'assistant'}]