单项选择题
A.(1) only
B.(2) only
C.both (1) and (2)
D.neither (1) nor (2)
单项选择题 If the chemical analysis of a lube oil sample taken from a diesel engine indicates an increased neutralization number, the （）.
单项选择题 When an auxiliary boiler is panting and emitting black smoke, you should （）.
单项选择题 With regards to a diesel engine crankcase explosion, the most violent is the（） (1) primary explosion (2) secondary explosion