单项选择题

Contour elevations on this chart refer to heights in feet above mean （）.

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

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单项选择题

Navigational charts are subject to frequent changes，the important ones of which are promulgated by （）.

A.Admiralty Notices to Mariners
B.Mariner's Handbook
C.Catalogue
D.Sailing Directions

单项选择题

No navigational aids are shown and the chart is not kept corrected for alterations in depths inside the pecked lines. For more detailed information，the larger scale charts must be （）.

A.referred to
B.appreciated
C.met with
D.concerned

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