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 is the drug of choice for antibiotic associated pseudomembranous enterocolitis? 
Select and explain. 
A. Linezolid, B. Oral vancomycin, C. Ciprofloxacin, D. Clindamycin
B: Oral vancomycin
Answer: B: Oral vancomycin 
Explanation: None