细水雾灭火系统的阀门应在系统压力达到（）％系统组件最大额定工作压力时开启。
A.90
B.85
C.80
D.95
参考答案：D
The hard-working peasants and their happy life _____ we saw in the countryside made a wonderful impression on us.
A．/
B．who
C．which
D．whom
征免性质栏应填( )。
A．100
B．101
C．201
D．501
