单项选择题
Fuel oil day tanks for diesel engines must be checked and cleaned and cleaned at regular intervals in order to remove（）
A.sludge B.water C.micro-organism growth D.all of the above
单项选择题 Excessively worn, or polished ends on a diesel engine valve spring, indicate（）
单项选择题 A loud clicking noise from the valve compartment of an operating diesel engine would indicate（）
单项选择题 In the cylinder of a diesel engine fuel is ignited by the（）
