单项选择题
The crankcase can not be opened （）the parts have been cooled down.
A.if B.as C.unless D.when
单项选择题 The crank throws are displaced from （） to obtained the same number of degrees between the different crank throws.
单项选择题 The crank pin journal is provided with large bores for （）.
单项选择题 The crank chamber oil （）.
