在全球经济发展中，（）的使用在整个能源中所占的比例越来越高。
A.一次能源
B.二次能源
C.合成能源
D.经济能源
参考答案：B
I didn't go to the movies yesterday because I the movie before. [ ]
A. had been watching
B. have seen
C. have watched
D. had seen
常见的电弧焊接缺陷有哪些？产生的主要原因是什么？
