单项选择题
A.They conduct heat poorly
B.They are expensive
C.They cannot be replaced
D.They require special tools for removal
单项选择题 When running a large, low-speed, main propulsion diesel engine on heavy fuel, which of the following precautions should be observed when switching back over to diesel oil?（）
单项选择题 Before shutting off the fuel supply to stop a medium or high–speed diesel engine, why is it necessary to allow the engine to idle for a few minutes?（）
单项选择题 Clogged diesel engine fuel oil filters can cause（）