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

If you are given the job of adding hydraulic fluid to a mooring winch, and are not certain as to the type of fluid to use, you should （）.

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

Low compressor head pressure in a refrigeration system can be caused by（）.

Pitting in the suction areas of a centrifugal pump bronze impeller is usually caused by （）.

Which of the following problems could cause the high pressure cutout switch to shut down the compressor in a refrigeration system?（）

If the head pressure of a reciprocating refrigeration compressor is excessive, （）.

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

One cause of high head pressure occurring in a refrigeration system can be （）.

A salinity indicator is used to determine the （）.