单项选择题
A.(1) only is correct
B.(2) only is correct
C.both (1) and (2) are correct
D.neither (1) or (2) are correct
单项选择题 In a normally operating diesel engine, the main cause of lubricating oil contamination in the crankcase is a result of the （）.
单项选择题 The amount of fuel injected in a particular time, or degree, of crankshaft rotation is termed （）.
单项选择题 A crankshaft whose center of gravity coincides with its center line is said to be （）.