This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology, Subject name: Pharmacology
[{'content': 'Best preparation of insulin for IV injection is:(1995) \nSelect and explain. \nA. Lente, B. Semi lente, C. Regular insulin, D. Humulin', 'role': 'user'}, {'content': 'Answer: C \nExplanation: cRef: KDT, 5th ed, p. 243, 240 & 4th ed, p. 271-269', 'role': 'assistant'}]