单项选择题
Each cylinder has one starting valve which is usually opened by air pressure and closed by （）
A.nuts and bolts B.new joints C.spring force D.sealing rings
单项选择题 Each crank is made up of two crank webs joined by a common（） to which the bottom endbearing is fitted.
单项选择题 During working, when the piston is near the （）, the air ignites the fine spray of fuel.
单项选择题 During the suction stroke, the piston is moving （）.
