This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Renal physiology, Subject name: Physiology
Which of the following ion is absorption in proximal convoluted tubule? 
Select and explain. 
A. Na+, B. Urea, C. K+, D. Mg+
A: Na+
Answer: A: Na+ 
Explanation: Maximum sodium reabsorption occours in PCT. Ref: Ganong's review of medical physiology; 24th edition; page no: 681