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
Which enzyme is a enzyme regulatory step in cholesterol synthesis? 
Select and explain. 
A. HMG CoA synthase, B. HMG CoA reductase, C. Phosphomevalonate kinase, D. Diphosphomevalonokinase
B: HMG CoA reductase
Answer: B: HMG CoA reductase 
Explanation: Ref: Textbook of Medical Biochemistry, Eighth Edition, Dr (Brig) MN Chatterjea Rana Shinde: page no: 431