混凝土裂缝产生的原因包括( )
A. 塑性收缩裂缝
B. 沉降收缩裂缝
C. 温度裂缝
D. 弹性变形
When to fasten the seat belt?
A. for take-off
B. for landing
C. during air turbulence
D. whenever the Fasten Seat Belt sign is on
发生紧急状况时,面罩会自动脱落,如果有小孩随行,应当先帮助小孩戴上氧气面罩,然后再自己戴。
A. 对
B. 错
How to put on the life vest?slip it over the head;fasten the buckles;pull the straps tight around the waist
A. 对
B. 错