顾客边吃东西边购物时，应（）其至收银台结账。
A.委婉提醒
B.引导
C.督促
参考答案：A
— Where is Bob? I cannot find him anywhere.
— He ________ have been off long. I heard him make a call just now. [ ]
A. shouldn't
B. can't
C. mustn't
D. needn't
插装阀通过控制油口的启闭和压力的大小，起（）控制阀的作用。
A、方向
B、压力
C、流量
D、温度
E、比例
