The type of extinguisher which should be used for an electric fire is ______.

A. carbon dioxide or foam
B. dry chemical or foam
C. carbon dioxide or dry chemical

Which of the following may hardness of the boiler water cause？

A. scale formation
B. corrosion
C. A and B

When pressure of lube. Oil has reduced lower than normal, the engine stops ().

A. automatically
B. automatic
C. automation

Before taking out the (),give the engine at least one complete turn.

A. steering gear
B. turning gear
C. timing gear

焊道与母材之间或焊道与焊道之间未完全熔化结合部分叫()。

采用碱性焊条一般使用()电源和短弧操作方法。

焊接接头冷却到较低温度时产生的焊接裂纹叫()。

焊接时，焊前应将焊缝及两侧20mm范围内，将油污、铁锈、水等清理干净。()

手弧焊时，焊接速度由焊工控制，其快慢对焊接质量无关。()

CO2焊接电源有直流和交流两种。()