阻塞性肺气肿产生低氧血症的主要机制是()
A.膈肌运动幅度降低
B.通气/血流比例失调
C.肺活量减少
D.肺总量减少
E.胸部活动受限
参考答案:B
Is Li Lei _____ school today?[ ]
A. in
B. at
C. on
D. by