工作斗的前部和下部应有防碰撞装置，装置接近或碰到障碍物时应自动停止臂架（梯架）的动作并有声音报警信号。
参考答案：对
X线发生效率的公式是
A．η=KV/Z
B．η=KVZ
C．η=KVZ2
D．η=KV2Z
E．η=K2VZ
Her husband earns ____ she while they do the same amount of work.
A．twice as many as
B．as twice much as
C．twice more money as
D．twice as much money as
