单项选择题
Particular care is needed when navigating in the vicinity of（）as very few of these features have been fully surveyed to modern standards to determine their correct position，full extent，or the least depth over them.
A.SW of Cocos Islands B.oceanic dangers or seamounts C.undiscovered dangers D.the continental shelf
单项选择题 On chart，bearings to near objects should be used in preference to objects farther off，because（）.
单项选择题 On a Mercator chart，1 nautical mile is equal to（）.
单项选择题 Every chart is liable to be incomplete（）.
