Sometimes lights are（）by fog，haze，dust，smoke，or precipitation which may be present at the light，or between the light and the observer，and which is possibly unknown by the observer.

Pilotage in this country is（）.A.Free of chargeB.Importa...

单项选择题Pilotage in this country is（）.

Mariners should ensure correct（）of aids to navigation d...

单项选择题Mariners should ensure correct（）of aids to navigation during twilight periods when some lighted aids to navigation are lit while others are not.

If the winch should fail while you are hauling in the a...

单项选择题If the winch should fail while you are hauling in the anchor，what prevents the anchor cable from running out（）.