单项选择题
A.ground the board
B.avoid reversing the polarity of the leads
C.isolate sensitive components with heat sinks
D.all of the above
单项选择题 The heated feedwater entering any flash chamber of a flash-type evaporator will（）
单项选择题 In a refrigeration system, which of the following statements describes the actions occurring when a solenoid valves, used in conjunction with an unloader head is energized?（）
单项选择题 The efficiency and output capacity of a low pressure distilling plant will be reduced if the last effect shell （）