单项选择题
A.cylinder covers
B.lubricating space
C.crosshead
D.exhaust manifold
单项选择题 Four strokes consist of suction, compression, （） and exhaust stroke.
单项选择题 For one or two types of engine,the piston and rod can be withdrawn downwards from the cylinder into the crankcase and then out through （）.
单项选择题 For one or two types of engine, the piston and rod can be withdrawn downwards from the cylinder into the crankcase and then out through the （）.