下列选项中不属于队列口令分类的是()。
A. 短促口令
B. 断续口令
C. 复合口令
D. 持续口令
The purpose of the wearing rings used in a centrifugal pump is to ().
A. prevent an internal explosion in the pump when it is overheated
B. enable a visual inspection of the pump while it is running
C. insure a proper alignment of the pump coupling to the driver
D. accommodate for friction between the impeller and the easing
利用信用卡消费后,如果退货的,特约单位也不能退还消费者现金。()
A. 正确
B. 错误
双伸缩立柱()作用是闭锁活柱下腔液体,使之不能回到小缸体的下腔。
A. 底阀
B. 安全阀
C. 液控阀
D. 气控阀