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單項選擇題

A heavy，thick-walled tube，usually steel，used between the drill pipe and the bit in the drill stem to weight the bit in order to improve its performance is called a（）.

A.heavy-walled drill pipe
B.tool joint
C.down hole tool
D.drill collar

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單項選擇題

A heavy steel curved arch constructed athwartships and above the after deck on a towing vessel is sometimes called a（）.

A.main brace
B.tow span
C.jockey bar
D.None of the above

單項選擇題

A head-on situation at night is one in which you see dead ahead a vessel showing（）.

A.one sidelight
B.one sidelight and a masthead light
C.one sidelight and two masthead lights
D.both sidelights of a vessel and her masthead light(s)