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
Opioid analgesic used in treatment of cough is ? 
Select and explain. 
A. Loperamide, B. Diphenoxylate, C. Codeine, D. Meperidine
C: Codeine
Answer: C: Codeine 
Explanation: None