This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Body composition and Acid base Balance, Subject name: Pediatrics
Respiratory acidosis is characterized by primary: 
Select and explain. 
A. Deficit of carbonic acid, B. Excess of carbonic acid, C. Deficit of bicarbonate, D. Excess of bicarbonate
B: Excess of carbonic acid
Answer: B: Excess of carbonic acid 
Explanation: Respiratory acidosis is caused by CO2 retention - excess carbonic acid.