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: Pharmacology
Which of the following drug acts as microsomal enzyme inhibitor: 
Select and explain. 
A. Rifampicin, B. Cimetidine, C. Phenobarbitone, D. Phenytoin
B: Cimetidine
Answer: B: Cimetidine 
Explanation: None