单项选择题
A.mark the position of a lost mooring
B.determine your vessel's sideslip underway
C.determine your speed through the water
D.indicate location of a man overboard
单项选择题 （）objects are those which stand out clearly from the background or other objects and are easily identifiable from a few miles offshore in normal visibility．
单项选择题 （）day，pilot flag should be displayed from main mast．
单项选择题 The heights and soundings of Admiralty chart are expressed（）in Fathoms（）in Meters．