单项选择题
A.the direct acting relief valve is used for controlling lower flows and pressure
B.the pilot operated relief valve is used for controlling higher flows and pressure
C.the pilot operated relief valve is used for controlling lower flows and pressure
D.the controlling accuracy of direct acting relief valve is worse than that of the pilot operated relief valve
单项选择题 In heavy marine engine the practice is to drive the engine on（）which has previously been stored in starting air reservoirs.
单项选择题 The water level of an exhaust gas boiler which is independent of the auxiliary boiler and just as the extra heating surface of it （）
单项选择题 For a given exhaust gas boiler, what is the quantity of its evaporation mainly determined?（）