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: Biochemistry
[{'content': 'To keep blood pH at 7.4, the HCO3 : H2CO3 ratio should be \nSelect and explain. \nA. 20:01, B. 30:01:00, C. 15:01, D. 1:01', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]