A swift current occurring in a narrow passage connecting two large bodies of water，which is produced by the continuously changing difference in height of tide at the two ends of the passage，is called a（）.

A slow，gradual fall of the barometer indicates approaching（）.

A stage should only be rigged（）.

A towing light is（）.

A time diagram is a diagram on the plane of the（）.

A tug may be in danger of tripping when（）.

A special daymark is a（）.

A twin-screw vessel with a single rudder is making headway. The engines are full speed ahead. There is no wind or current. Which statement is FALSE? （）

A tow that is properly aligned to pass through a narrow opening between two bridge piers is “ （）”.

A tug is “in irons” when held in a fixed position by（）