焊渣的更重要作用是与熔化金属产生物理化学反应或添加合金元素，（）焊缝的金属性能。
A.调节
B.消除
C.改善
参考答案：C
Our computer ________ at nine this morning and we haven't been able to do anything. [ ]
A. has broken down
B. crashed
C. has gone wrong
D. was out of order
永久气体气瓶充装压力一般远大于低压液化气体，所以充装过量的危害（）低压液化气体。
A、大于
B、小于
C、无法比较
