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單項(xiàng)選擇題

Conditions for crossing a rough bar are usually best at （）.

A.low water slack
B.high water slack
C.high water ebb
D.high water flood

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單項(xiàng)選擇題

Clearances of bridges and overhead cables below Bonneville Dam refer to heights in feet above mean （）.

A.lower low water
B.high water
C.low water
D.sea level

單項(xiàng)選擇題

Clearance gauges at bridges indicate （）.

A.the height of the tide
B.depth of water under the bridge
C.charted vertical clearance at mean low water
D.distance from the water to low steel of the bridge