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

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

The rate of heat transfer between the hot and cold fluids passing through a shell-and-tube type heat exchanger will （）.

A salinity indicator is used to determine the （）.

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

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

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

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 （）.

When the steering gear is in operation, you should （）.