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': 'Which of the following is least permeable in an excitable tissue at rest? \nSelect and explain. \nA. Na+, B. K+, C. Cl-, D. Ca2+', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The ratio of permability between K : Cl : Na is 1: 0.45 : 0.04.', 'role': 'assistant'}]