单项选择题

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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单项选择题
A disadvantage of using chain lashing on heavy vehicles aboard Ro-Ro vessels is that it is （）.

A.heavy
B.easily damaged
C.affected by temperature
D.costly relative to the strength ratio
单项选择题
A device fitted over the discharge opening on a relief valve consisting of one or two woven wire fabrics is called a flame（）.

A.stopper
B.screen
C.filter
D.restrictor
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