The luminous range of a light takes into account the（）.……

单项选择题Restricted areas at locks and dams are indicated by（）.

A.flashing red lights upstream and fixed red lights downstream
B.yellow unlighted buoys
C.signs and/or flashing red lights
D.red daymarks upstream and green daymarks downstream

单项选择题Preferred channel buoys indicate the preferred channel to transit by（）.

A.odd or even numbers
B.the color of their top band
C.the location of the buoy in the channel junction
D.the buoy's light rhythms

单项选择题Lighted white and orange buoys must show which color light?（）

A.Orange
B.White
C.Red
D.Alternating yellow and white

单项选择题In plotting a running fix，how many fixed objects are needed to take your lines of position from? （）

A.Three
B.Two
C.One
D.None

单项选择题At the magnetic equator there is no induced magnetism in the vertical soft iron because（）.

A.the lines of force cross the equator on a 0°-180°alignment
B.the quadrantal error is 0°
C.there is no vertical component of the Earth's magnetic field
D.the intercardinal headings have less than 1°