A.Strong low pressure B.Strong high pressure C.Steep pressure gradient D.Steep gradient pressure
单项选择题Isobars on a synoptic chart are useful in predicting（）.
A.temperature B.dew point C.wind velocity D.relative humidity
单项选择题When a wind blows round clockwise，it is（）.
A.Variable B.Changing C.Backing D.Veering
