A weather forecast states that the wind will commence backing. In the Northern Hemisphere，this would indicate that it will（）.

单项选择题A tropical wave is usually preceded by（）.

A.tropical storms
B.good weather
C.heavy rain and cloudiness
D.heavy seas

单项选择题A tropical wave is located 200 miles due west of your position，which is north of the equator. Where will the wave be in 24 hours? （）

A.Farther away to the west
B.Farther away to the east
C.In the same place
D.Closer and to the west

单项选择题A tropical storm is building strength some distance from your ship. Waves are coming from the east，with periods increasing from 5 seconds to 15 seconds. The swell is from the east. Where was the storm when these new swells were generated? （）

A.To the north of you
B.To the south of you
C.To the east of you
D.To the west of you

单项选择题A tropical cyclone has recurved and entered temperate latitudes. In the Northern Hemisphere when a large high pressure system lies north of the storm，what situation may occur?（）

A.The low may suddenly deepen，and the cyclone intensify and pick up speed
B.The left semicircle may become the dangerous semicircle
C.The low and the high may merge and cancel out the weather characteristics of each
D.The high may force the cyclone to reverse its track

单项选择题A sylphon cell is a part of a（）.

A.maximum thermometer
B.barograph
C.thermograph
D.hygrometer