支气管扩张发病的机制是（）
A.支气管一肺组织感染及阻塞
B.肺结核
C.肿瘤压迫
D.支气管先天性发育缺损和遗传因素
E.支气管内结石
参考答案：A
What these young men were doing（）a threat to the safety of the whole neighborhood.
A.constructed
B.contracted
C.constituted
D.contributed
电气化区段内，信号干线电缆终端应注意什么？
