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: Physiology
[{'content': 'Anion gap is mostly due to \nSelect and explain. \nA. Proteins, B. Sulphates, C. Phosphates, D. Nitrates', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Anion gap is mainly caused by plasma albumin.', 'role': 'assistant'}]