A salinity indicator is used to determine the （）.

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 （）.

An internal bypass is provided on some hydraulic system suction strainers to help reduce the possibility of （）.

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

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

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

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

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

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