氧气切断阀间为何要充入N1?
参考答案:
充氮的作用是防止氧气泄漏,造成后系统O2含量超标,气化投料后造成爆炸。
Many kinds of birds fly south at the _____ of winter. [ ]
A. sight
B. approach
C. direction
D. access
什么是相电流、相电压和线电流、线电压