If the relief valve on the discharge side of a hydraulic pump lifts, the cause could be （）.

Which of the following statements is correct concerning heat transfer?（）

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

On tank vessels equipped with power operated cargo tank valves, the type of power operator most commonly used is （）.

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

The general purpose of a heat exchanger is to （）.

A salinity indicator is used to determine the （）.

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

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

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