Which of the listed pumps is NOT a positive displacement pump?（）

The temperature differential occurring between the inlet temperature of the fluid to be cooled and the outlet temperature of the cooling medium in a shell-and-tube heat exchanger is greatest in which of the flow designs listed?（）

When a refrigeration compressor has developed a high head pressure as a result of a refrigerant overcharge, you should （）.

An excessive charge of refrigerant in an air-cooled refrigeration system can cause （）.

If the suction pressure at the refrigeration compressor is below normal, the cause can be（）.

The usual symptoms of cavitation in a centrifugal pump is （）.

An increasing head pressure in a refrigeration system, without any corresponding change in the cooling water inlet temperature, would probably be caused by （）.

A pressure drop through the refrigerant liquid line may cause （）.

The control mode in which the final control element is moved from one of two flexed positions to the other is known as （）.

Heavy wear in a particular area of the inner circumference of a packing ring may be caused by （）.