This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of lipid, Subject name: Biochemistry
[{'content': 'Which enzyme is a enzyme regulatory step in cholesterol synthesis? \nSelect and explain. \nA. HMG CoA synthase, B. HMG CoA reductase, C. Phosphomevalonate kinase, D. Diphosphomevalonokinase', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ref: Textbook of Medical Biochemistry, Eighth Edition, Dr (Brig) MN Chatterjea Rana Shinde: page no: 431', 'role': 'assistant'}]