This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory System, Subject name: Physiology
Normal diffusion of CO2 at rest- 
Select and explain. 
A. 20-25 mL/min/mm Hg, B. 50-100 mL/min/mm Hg, C. 100-200 mL/min/mm Hg, D. 300-400 mL/min/mm Hg
D: 300-400 mL/min/mm Hg
Answer: D: 300-400 mL/min/mm Hg 
Explanation: Ans. (d) 300-400 ml/min/mm Hg(Ref: Ganong, 25th ed/p.640)Normal value of DLCO is 25 mL/min/mm HgDiffusion coefficient of O2 is about 1.23 times that of COSo, Diffusing capacity for oxygen is 25*1.23=30mL/min/mmHgDiffusion capacity of CO2 is 400 ml/min/mm Hg