单项选择题
A.Right Descending Bank span
B.Left Descending Bank span
C.Center span
D.Water is equal under all spans
单项选择题 After the passage of a cold front the visibility（）.
单项选择题 After the initial cleaning of flue gas in an inert gas system the gas is passed through what device for final cleaning?（）
单项选择题 After sending a message describing the symptoms of an ill crew member，you receive a message containing the code MRL. This means “（）”.