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: Physiology
[{'content': 'C-peptide occurs in: \nSelect and explain. \nA. Proinsulin, B. Glucagon, C. Parathormone, D. Thyroxine', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Preproinsulin\xa0contains\xa0a\xa0signal\xa0peptide\xa0of 23\xad-amino\xa0acid. The\xa0signal\xa0peptide is removed\xa0as it\xa0enters\xa0the\xa0endoplasmic\xa0reticulum.\xa0The remainder\xa0of\xa0the\xa0molecule\xa0is\xa0pro-insulin. This\xa0peptide contains A,\xa0B\xa0chains\xa0 and\xa0the connecting peptide (C peptide). Separation\xa0of C peptide produces insulin.', 'role': 'assistant'}]