采煤工作面移动刮板输送机时,必须有()的安全措施。
A、防止冒顶
B、防止顶伤人员
C、防止损坏设备
D、防止输送机弯曲
参考答案:A, B, C
The railway bridge ___________ by 2015 will provide a faster route to transport goods.
A.to be completed
B.is completed
C.completed
D.being completed
区域体层,系指照射角应小于()
A.5°
B.10°
C.15°
D.20°
E.30°