单项选择题
Each journal and pin should be examined for （） and grooving.
A.bridges B.recesses C.rears D.ridging
单项选择题 Each cylinder liner on the marine medium speed engines （）.
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 （）
