单项选择题 The four-stroke cycle is so called because it takes （） to complete the processes needed to convert the energy in the fuel into work.

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.