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

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

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

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

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

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

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 following statements is correct concerning heat transfer?（）

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