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
Anion gap is mostly due to 
Select and explain. 
A. Proteins, B. Sulphates, C. Phosphates, D. Nitrates
A: Proteins
Answer: A: Proteins 
Explanation: Anion gap is mainly caused by plasma albumin.