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': 'Most essential medicines should be formulated as: \nSelect and explain. \nA. No compound, B. Single compound, C. Multiple compounds, D. Fixed dose combinations', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]