The light is on in Mr. Green's room. He _______ be at home. [ ]

A. must

B. can

C. mustn't

D. can't

慢性阻塞性肺疾病发生呼吸衰竭的主要机理是

A．弥散功能障碍

B．通气/血流比例失调

C．静-动脉分流增加

D．肺泡通气不足

E．肺泡萎陷