單項選擇題A type of precipitation that occurs only in thunderstorms with strong convection currents that convey raindrops above and below the freezing level is known as（）.

A.sleet
B.hail
C.freezing rain
D.rime


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1.單項選擇題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.If one screw is stopped，the ship will turn toward the side of the stopped screw
B.The principal force which turns the ship is set up by the wake against the forward side of the rudder
C.Turning response by use of the rudder only is greater than on a single-screw vessel
D.With the rudder amidships，the ship will steer a fairly steady course

2.單項選擇題A tug may be in danger of tripping when（）.

A.towed sideways by an overwhelming force on the towline
B.her tow moves parallel to and forward on either side of the tug
C.the tow is no longer directly astern but moves up on her quarter
D.All of the above

3.單項選擇題A tug is best positioned for towing and maneuvering on rivers and other restricted waters where wave action is limited when（）.

A.directly astern and pushing the tow
B.towing on a hawser
C.towing alongside and parallel to the vessel it is towing
D.towing on the hip

4.單項選擇題A tug is “in irons” when held in a fixed position by（）

A.the weight of its tow，its being anchored，or grounded
B.the weight of its towing hawser on the bottom
C.an adverse current
D.lack of power or an engine breakdown

5.單項選擇題A tug in irons is（）.

A.rudder bound
B.being tripped by the towline
C.unable to maneuver
D.broached