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': 'Kidney plays a role in maintaining constancy of milieu interior. Milieu interior refers to: \nSelect and explain. \nA. ECF, B. ICF, C. Plasma, D. Serum', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Milieu interior refers to the extracellular environment. The main function of kidney is homeostasis, the maintenance of the constancy of the milieu interior. Ref: Fundamentals of Medical Physiology by Joel Michael, Sabyasachi Sircar, 2010, Chapter 53.', 'role': 'assistant'}]