单项选择题
When visibility is reduced to about 5 miles, we say that visibility is（）.
A.very good B.good C.poor D.moderate
单项选择题 When your vessel is proceeding to the area of traffic density,（）is used to determine the exact ranges of other ships or objects in the vicinity.
单项选择题 Which is wrong?（）.
单项选择题 While（）,they met with a storm weather.
