The main merit of a multi cylinder type cylinder sleeve is

smaller engine dimensions

better cooling efficiency

high rigidity

none of these

balance the timing in the movement of the two groups of pistons

increase inertia force of the rotating crankshaft

reduce vibrations caused by the crankshaft rotation

adjust the timing of the intake and exhaust valve openings

returns cylinder head lubricating oil to the oil pan at high speed

turns oil into fine mist for spray lubrication

regulates the pressure of engine oil supplied by the oil pump for the lubrication of cylinder head mechanism and other purposes.

removes impurities from cylinder head lubricating oil

diameter and above

displacement and efficiency

bore and stroke

bore and length

volume of the cylinder

length of the connecting rod

internal diameter of the cylinder

distance between T.D.C and B.D.C