单项选择题
A.is usually cooled by sea water
B.can be replaced when worn out
C.is in direct contact with the water in the bore of the cylinder
D.can t expand when heated
单项选择题 Each cylinder is closed at the top by a （）, made of a special heat-resistant steel.
单项选择题 Each cylinder has one starting valve which is usually opened by air pressure and closed by （）
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.