单项选择题 The purpose of the skirt or trunk in four-stroke cycle engines is to act in a similar manner to a （）.

单项选择题 Medium speed engines have a （） power to weight ratio than the slow speed two strokes, but due to the higher speeds tend to have （） maintenance intervals.

单项选择题 （） allows the engine to be placed wherever is most suitable, as they no longer have to be aligned with reduction gearing and shafting as is the case with conventional installations.