单项选择题
Which information does the outer ring of a compass rose on a nautical chart provide（）.
A.variation B.true directions C.magnetic directions D.annual rate of variation change
单项选择题 Which chart symbol indicates the bottom is clay（）.
单项选择题 Where would you obtain data on currents for areas of the world not covered by the National Ocean Service（）.
单项选择题 The soundings on the imperial chart are measured in（）.
