螺栓冷紧
参考答案：
介质温度低于-20℃的管道的螺栓，除在施工时紧固外，还要在达到工作温度或规定温度时再进行的紧固。
．We are taught that a business letter should be written in a formal style ____ in a personal one．
A．less than
B．other than
C．better than
D．rather than
运费（）
A. 502/2560/3
B. 502/2560/2
C. 502/2560/1
D. 2560/1
