A.west in west longitude and east in east longitudeB.ea……

单项选择题During a period of whiteout，you should expect which of the following（）.

A.Snowfall or blowing snow
B.Lack of ability to estimate distance
C.Harsh contrast between sun-illuminated snow cover and the background
D.Hazy horizons with extensive mirage effects

单项选择题Due to lapse of time the risk in these areas to surface navigation is now considered （）than the ordinary risks of navigation，but a very real risk still exists with regard to anchoring，fishing or any form of submarine or seabed activity.

A.more serious
B.not less serious
C.more dangerous
D.no more dangerous

单项选择题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

单项选择题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

单项选择题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