【简答题】Look at the picture, the electrode, the arc and the weld pool are sorrounded by the shielding gas. They have no chance to contact with air before the molten metal cools down and solidifies. That`s to ...
【单选题】研究吸烟和肺癌的关系,队列研究开始,基线资料收集时,判断研究对象是否患有肺癌的目的是
【简答题】A.Avoiding B.Fending C.Escaping D.Shielding
【简答题】A. Avoiding B. Fending C. Escaping D. Shielding