单项选择题
In the closed cooling system, the water （）.
A.is made to circulate out of the system B.is made to circulate within the system C.is made circulate within the system D.is made circulate out of the system
单项选择题 If the temperature drops low enough, oil will not flow, （） just tell us the temperature.
单项选择题 The （） can tell us how much heat we can get from the burning of an oil.
单项选择题 （） into the cylinder because no fuel can burn （） it.
