钢材的性能不仅取决于钢材的化学成分，而且取决于钢材的()。
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18MnMoNb钢的焊接性较差.焊前需要预热，预热温度为()℃。
A. 180~250
B. 250~280
C. 280~320
D. 320~350
氩气瓶是一种钢制圆柱形高压容器，其外表涂成()。
A. 浅蓝色
B. 银灰色
C. 深黑色
D. 深绿色
钨极氩弧焊焊不锈钢时电源种类和极性应采用()。
A. 交流方波电源
B. 交流电源
C. 直流正接
D. 直流反接
可以先解开他的衣领，让他侧卧，然后打电话叫救护车
A. The security may open his coat, let him lie on his side and ring the bell
B. The security may lock his collar, let him lie on his side and ask for help
C. The security should let him lie on his side while unlocking his clothes and waiting for the ambulance
D. The security may unlock his collar, let him lie on his side and call an ambulance
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