焊机外壳和不带电部分应接地(或接零)。
参考答案：对
分子、分母是不同合数的分数，那么[ ]
A．一定是最简分数
B．一定不是最简分数
C．不一定是最简分数
We should learn the others, because everyone has his advantages. [ ]
A. with
B. for
C. from
D. about
