Which of the problems listed would came the discharge temperature of an R-12 refrigeration compressor to increase?（）

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

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

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

The output volume of a positive fixed displacement pump can be changed only by （）.

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

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

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

Who is responsible for ensuring that someone is assigned to close the watertight doors in an emergency?（）

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