A.coming cold weather conditionsB.a warm front weather ……

单项选择题Snow has obliterated surface features and the sky is covered with uniform，altostratus clouds. There are no shadows and the horizon has disappeared. What is this condition called? （）

A.Ice blink
B.Whiteout
C.Water sky
D.Aurora reflection

单项选择题Relative humidity is the percentage of water vapor that is in the air as compared to the maximum amount it can hold at（）.

A.a specific barometric pressure
B.a specific temperature
C.a specific wind speed
D.any time

单项选择题Recurvature of a hurricane’s track usually results in the forward speed（）.

A.increasing
B.decreasing
C.remaining the same
D.varying during the day

单项选择题Prevailing winds between 30°N and 60°N latitude are from the（）.

A.north
B.south
C.east
D.west

单项选择题Plain language is usually used on marine weather（）.

A.forecasts
B.observations
C.analyses
D.reports