如何建构主义教学观。

A. 设备没有收到光信号
B. 光口工作正常
C. 光信号帧失步
D. 光路误码

A. 供电电压提高一倍，更能适应大功率负荷的供电，功率输送能力
B. 牵引网结构简单，投资少，维护费用低
C. 牵引网阻抗低
D. 可以有效降低对通讯线路的干扰。

A. to avoid the rearrangement of the cargo loaded on board
B. to ensure the safety of the ship and cargo
C. to reject the damaged cargo during loading operation
D. to prevent the spontaneous combustion of coal and grai