单项选择题
A.natural circulation of the water in the water tube boiler is better than that in the fire tube boiler
B.for the same output the water tube boiler will carry less mass of water compared with the fire tube boiler
C.the water tube boiler will cost shorter time for steam raising
D.the water tube boiler require lower skill in operating and maintaining
单项选择题 Which one of following statement is not true concerning the suitable sites of the direct acting relief valve and the pilot operated relieve 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 （）