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

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An excessive charge of refrigerant in an air-cooled refrigeration system can cause （）.

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

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

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

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