单项选择题
A.Heat is given off from a high temperature region known as a heat sink
B.Heat transfer rate is affected most by the size of the heat sink involved
C.Heat transfer rate is affected most by the temperature difference between the heat source and the heat sink
D.Heat transfer by radiation will occur only by mass motion of a fluid substance
单项选择题 Who is responsible for ensuring that someone is assigned to close the watertight doors in an emergency?（）
单项选择题 The rate of heat transfer from a hot region to a cold region is affected most by the （）.
单项选择题 A gradual decrease in the discharge pressure of an operating hydraulic pump can be caused by （）.