COPD最常见的病因为()
A．空气污染
B．吸烟
C．呼吸系统反复感染
D．营养不良
E．遗传因素
参考答案：B
—Mom,can I go to play football now?
—No,you finish your homework first.[ ]
A. must
B. can
C .could
D. may
乙状结肠系膜
