二氧化碳灭火系统当采用火灾探测器时自动控制应在接收到()个独立火灾信号后才能启动。
A、1
B、2
C、3
D、4
参考答案：B
The manager was worried about the press conference his assistant _____in his place but ,luckily ,everything was going on smoothly.
A．gave
B．gives
C．was giving
D．had given
硫磺回收装置紧急停车后，开车时对燃烧炉点火时（）。
A、先点火再启风机
B、先启风机
C、先开启酸气进炉阀
D、先开燃料气进炉阀
