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（）.
单项选择题 Lighted white and orange buoys must show which color light?（）
单项选择题 In plotting a running fix，how many fixed objects are needed to take your lines of position from? （）
