管理信息系统的空间分布结构中，______结构安全和可靠性相对较高，可根据应用需要和

The Internet connection for the entire area _________ when there was a sudden power cut yesterday.[ ]

A. lost            

B. was lost      

C. had lost          

D. had been lost  

Too often teachers' ______ with parents are devoted to petty accounts of children's misbehaviors, complaints about laziness and poor work habits and suggestion for penalties and rewards at home.

A．acquaintance

B．association

C．conferences

D．collaboration

当泵轮与涡轮转速差较大时，形成（），当泵轮与涡轮转速接近时，形成（）。

煤气管道进行强度和严密性试验时的试验介质是（）。

A．水

B．煤气

C．二氧化碳

D．空气

精神文化层是企业文化的中间层次，集中体现了企业文化的精神层对员工和企业组织行为的要求。