低压分离器利用（）来进行气密
A、反应系统氮气气密的余压
B、用高压蒸汽
C、用高压车注入压缩空气
D、反应系统氢气气密的余压
参考答案：A
The most important thing ______ we should consider is the first idea _____ he has mentioned in the speech.
A．which; that
B．that; which
C．which; which
D．that; that
合法行为和违法行为都可以引起法律关系的产生，变更和消灭。 ( )
