单项选择题
The four standard light colors used for lighted aids to navigation are red，green，white，and （）.
A.purple B.orange C.blue D.yellow
单项选择题 The equator is（）.
单项选择题 Restricted areas at locks and dams are indicated by（）.
单项选择题 On a chart，the characteristic of the light on a lighthouse is shown as flashing white with a red sector.The red sector（）.
