单项选择题 A centrifugal pump produces flow with a resulting discharge head by energy conversionIt is typical for the energy conversion to follow the order of （）.

单项选择题 If an operating bilge pump is developing good vacuum, but is unable to discharge any water, which of the following problems is the most probable cause?（）

单项选择题 The sudden reduction of pressure occurring within the crankcase of a refrigeration compressor during starting causes the （）.