行程（运行）限位器
参考答案：
保证运行机构在其运动的极限位置时能自动切断电源，并停止运行的装置。
We set no limit to the _______ you can make to support children in the poor areas. Big or small, it shows your concern for them.
A．generosity
B．choice
C．donation
D．contribution
接地引入线不宜超过30m，宜采用（）的热镀锌扁钢.
A.20mm*2mm
B.30mm*3mm
C.40mm*4mm
D.60mm*6mm
