手工电弧焊焊条有几部分组成？各有何作用。
参考答案：
药皮：造气造渣、调节焊缝的合金成分
焊芯：传导电流和填充焊缝金属
A violent earthquake hit Japan on March 11, 2011, _____ tens of thousands of deaths. [ ]
A. having caused
B. causing
C. caused
D. to cause
法律体系
