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: Medicine
[{'content': 'A 2 year old child is being evaluated for persistent metabolic acidosis. Blood tests show Na+ 140 mEq/I, K+ 3 mEq/I, Ca2+ 8 mg/dL, mg2+2 mg/dL, phosphate 3 mg/dl, pH 7.22, bicarbonate 16 mEq/I and chloride 112 mEq/I. The plasma anion gap is - \nSelect and explain. \nA. 9, B. 15, C. 22, D. 25', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]