单项选择题
Which of the devices listed is common to all types of pumps?（）
A.A power end and fluid end B.A propeller and educator C.A volute and impeller D.A turbine and piston
单项选择题 A centrifugal pump may fail to deliver water when first started if the （）.
单项选择题 Which features of a centrifugal pump reduce the need for renewing worn impellers and pump casings?（）
单项选择题 When securing a flash-type evaporator for an extended period of time, you should （）.
