单项选择题
A.one B.fifteen C.sixty D.ninety
The crank-room cover should not be opened until at leas...
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
The crankcase cover should never be allowed to open for...
单项选择题The crankcase cover should never be allowed to open for investigation when （）
A.the engine stops B.the engine is running C.you repair the engine D.overhauling the engine
The crankcase can not be opened （）the parts have been c...
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
