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單項選擇題

A drilling bit which is doughnut shaped to permit recovery of the center portion of the hole drilled is called a（）.

A.diverter bit
B.hole reamer
C.core bit
D.conventional bit

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單項選擇題

A drawbridge may use visual signals to acknowledge a vessel’s request to open the draw. Which signal indicates that the draw will NOT be opened immediately?（）

A.A flashing amber light
B.A fixed red light
C.A white flag raised and lowered vertically
D.A flashing white light

單項選擇題

A Doppler speed log indicates speed through the water（）.

A.at all times
B.in the bottom return mode
C.in the volume reverberation mode
D.only when there is no current

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