单项选择题
Two navigational hazards are located near to each other，but each is marked by an individual cardinal buoyage system. The buoys of one cardinal system may be identified from the other system by（）.
A.the differing light colors B.one system having odd numbers while the other system has even numbers C.one system using horizontal bands while the other system uses vertical stripes D.the difference in the periods of the light
单项选择题 This is（）where we shall anchor.
单项选择题 There is sufficient anchorage for（）at all time around the No.1 buoy and for smaller vessels around the No.4 buoy.
单项选择题 The shortest distance between any two points on earth defines a（）.
