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: Microbiology
[{'content': 'Soluble components of complement system account for about \nSelect and explain. \nA. 1-2 mg/ml of total serum protein, B. 3-4 mg/ml of total serum protein, C. 5-7 mg/ml of total serum protein, D. 7-8 mg/ml of total serum protein', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]