单项选择题
（）are published for the correction of Admiralty Charts．
A.Admiralty Sailing Directions B.Admiralty List of Signals C.Mariner's Handbook D.Admiralty Notices to Mariners
单项选择题 A chart has extensive corrections to be made to it. When these are made and the chart is again printed，the chart issue is a （）.
单项选择题 Charts are subject to frequent correction according to （）.
单项选择题 Contour elevations on this chart refer to heights in feet above mean （）.
