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

The general purpose of a heat exchanger is to （）.

If the relief valve on the discharge side of a hydraulic pump lifts, the cause could be （）.

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

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

The rate of heat transfer from a hot region to a cold region is affected most by the （）.

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

A salinity indicator is used to determine the （）.

The major source of chemical contaminants in hydraulic fluid is （）.

A grease gun is generally used to lubricate a （）.