单项选择题 The pumps employed on board ship can be divided into two main categories ie（） pumps and centrifugal pumps.

单项选择题 The pump has a constant stroke and the amount of fuel delivered is regulated by rotating （） which has a specially arranged helical groove cut into it.

单项选择题 The projection on a shaft designed to change circular motion into up and down or back and fore motion is called （）.