A large valve，usually installed above the ram preventers，that forms a seal in the annular space between the pipe and wellbore or，if no pipe is present，on the wellbore itself is called the（）.

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（）.

A.flame arrestor
B.flame screen
C.detonation arrestor
D.detonation blocker

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（）.

A.slipway
B.graving dock
C.ground warp
D.caisson dock

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

A.a 2-second blast every 20 seconds
B.a 4-second blast every 20 seconds
C.an 8-second blast every 30 seconds
D.a 10-second blast every 30 seconds

单项选择题A jack-up drilling rig being towed must（）.

A.turn off all lights that interfere with the navigation lights
B.turn on all available working lights on deck
C.ring the bell rapidly for five seconds once a minute
D.display two black diamonds in a vertical line during the day

单项选择题A helmsman receives the command “Right 15 degrees rudder.”The helmsman’s IMMEDIATE reply should be（）.

A.Aye Aye Sir
B.Right 15 degrees rudder
C.Rudder is right 15 degrees
D.No reply is necessary，just carry out the order