焊条电弧焊使用的焊接电缆必要时可用扁铁搭接或用其他办法来代替连接焊接的电缆。()
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在空气中产生电弧要有三个必要条件：即气体电离、电极熔化及电子发射。()
The "dark side" (Para. 5) implies that modern agriculture will _____.
A. have a great impact on the U.S. economy development
B. lead to ecology pollution, if improperly controlled
C. have to decrease the soil erosion
D. change the DNA of conventional species
焊工在施焊时必须穿戴好防护用品，夏季可以卷起袖口，穿短袖衣及敞开衣服等进行电焊工作。()
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