单项选择题
A.size of the heat sink
B.temperature difference between the regions
C.size of the heat source
D.total heat of the system
单项选择题 A gradual decrease in the discharge pressure of an operating hydraulic pump can be caused by （）.
单项选择题 If you are given the job of adding hydraulic fluid to a mooring winch, and are not certain as to the type of fluid to use, you should （）.
单项选择题 The output volume of a positive fixed displacement pump can be changed only by （）.