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

The amount of fluid friction or internal friction inherent in a mineral lubricating oil is reflected as a measure of its （）.

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

If the viscosity of the liquid being transferred remains constant as the discharge pressure increases, the rotary pump （）.

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

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

A gradual decrease in the discharge pressure of an operating hydraulic pump can be caused by （）.

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（）.

A salinity indicator is used to determine the （）.