The population level in this area has        during the past 12 years. [ ]

A.expanded

B.exploded

C.explored

D.extended

当喷嘴阀全开，而进口压力仍然高于设定压力时，控制器打开（）泄压

A、阶梯阀

B、压力开关

C、差压控制阀

D、喷嘴阀