单项选择题
The crank-room cover should not be opened until at least （） minutes after the engine stops.
A.10 B.15 C.20 D.30
单项选择题 The crankcase cover should never be allowed to open for investigation when （）
单项选择题 The crankcase can not be opened （）the parts have been cooled down.
单项选择题 The crank throws are displaced from （） to obtained the same number of degrees between the different crank throws.
