属于急性支气管炎的病因是
A.病毒感染
B.细菌感染
C.病毒和细菌、肺炎支原体混合感染
D.免疫功能低下、营养障碍、支气管局部结构异常
E.结核杆菌感染
参考答案:A,B,C,D
— What should we do first if we want to develop our country?
— A lots of roads , I think. [ ]
A. have built
B. must be built
C. must build
D. have to build
井下()区域应设置禁止通行标志。
A、井下轨道大巷
B、危险区
C、爆破警戒处
D、不兼作行人的绞车道