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? （）

Relative humidity is the percentage of water vapor that...

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（）.

Recurvature of a hurricane’s track usually results in t...

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

Prevailing winds between 30°N and 60°N latitude are fro...

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