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 （）.
A.first edition B.new edition C.revised edition D.reprint
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 （）.
单项选择题 Navigational charts are subject to frequent changes，the important ones of which are promulgated by （）.
