单项选择题 High firing pressures and a low exhaust temperature in a diesel engine may result from （）.

单项选择题 Whether using a centrifuge or a simple filter, oil cleaning and filtration will be the most effective when the oil is at a （）.

单项选择题 Exhaust valve grooving and corrosion is caused by certain components of residual fuel oilThese components are sodium, sulfur, and （）.