单项选择题 A large metallic device，mounted directly in the piping (usually located at the dock near the point where the vapor hose is attached)，designed to prevent the passage of a rapidly moving flame through the piping is called a（）.

单项选择题 A large basin cut into the shore，closed off by a caisson，and used for dry docking of ships is known as a（）.

单项选择题 A jack-up drilling unit elevated on the Outer Continental Shelf must have a fog horn that will sound（）.