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
[{'content': 'Atropine is added to commercial preparations containing diphenoxylate to: \nSelect and explain. \nA. Potentiate its anti-spasmodic effect, B. To reduce excretion of salt and water, C. To prevent overdosage and discourage opioid dependence, D. To prolong its duration of action', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]