渠道管理的实质是什么？
当离心泵叶片入口附近的最低压强（）输送温度下液体的饱和蒸气压，就会发生气蚀现象。 ["等于","小于","等于或小于","大于"]
Which of the following problems may occur if the opening pressure of a fuel injection nozzle is greater than specified by the engine manufacturer?（） ["The amount of fuel injected will be increased","The start of injection will be retarded","The nozzle will permit fuel to dribble","The spray pattern will be distorted"]
对输送酸、碱以及易燃、易爆、有毒液体的泵，要求采用（）轴封装置。 ["A.填料密封","B.液压密封","C.气压密封","D.机械密封"]
在Excel 2003中使用自动套用格式时必须完全按照系统提供的格式套用，不能做任何改动。
简述虾维生素C缺乏病的诊断方法。
