钨板氩弧焊的电极材料,目前主要有纯钨钍钨和()等三种。
参考答案:铈钨
The box is heavy I can't lift it. [ ]
A. too; to
B. so; that
C. very, that
D. too; that
分光光度分析法依据的原理是()。
A.亨利定律;
B.朗伯-比尔定律;
C.欧姆定律;
D.库仑定律。