单项选择题
A.supplying high pressure oil into a hydraulic motor
B.supplying high temperature air into the cylinder
C.supplying high pressure air into the cylinder
D.electrical igniting
单项选择题 In modern installations, the main engine and the standby auxiliary engines（）
单项选择题 In order to maintain a constant outlet water temperature of 80-85℃ from the engine, a three-way valve is installed（）
单项选择题 About the jacket water, that of the auxiliary engines usually（） is circulated by pumps, and the main engine usually （）