单项选择题
An integral part of a blowout preventer that serves as the closing element on an open hole，and whose ends do not fit around the drill pipe but seal against each other and shut off the space below completely is the（）.
A.shear ram B.blind ram C.pipe ram D.annular ram
单项选择题 An example of a modern anchor which has a stock is a(n)（）.
单项选择题 An example of a messenger is a（）.
单项选择题 All electrical appliances aboard a vessel should be grounded to（）.
