单项选择题
A single fitting installed in a pipeline that either blanks off the pipe or allows a full flow passage of a liquid through the pipe is referred to as a（）.
A.blind flange B.pivot coupling C.quick-release coupling D.spectacle flange
单项选择题 A set of interior steps on a ship leading up to a deck from below is known as（）.
单项选择题 A measurement device for inspecting anchor chain is the（）.
单项选择题 A design modification of an anchor chain which prevents kinking is the（）.
