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
Hyponatremia is defined as a serum Na+ level 
Select and explain. 
A. < 135 mmol/L, B. > 135 mmol/L, C. < 160 mmo/L, D. < 100 mmo/L
A: < 135 mmol/L
Answer: A: < 135 mmol/L 
Explanation: None