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 set of interior steps on a ship leading up to a deck ...

单项选择题A set of interior steps on a ship leading up to a deck from below is known as（）.

A measurement device for inspecting anchor chain is the...

单项选择题A measurement device for inspecting anchor chain is the（）.

A design modification of an anchor chain which prevents...

单项选择题A design modification of an anchor chain which prevents kinking is the（）.