下列图形不是中心对称图形的是（   ）.

风向是风的____。风向为“北”，表示风来自____。风力是风的____，共分____级。

    Mike lives in Guangzhou. His friend Tom lives in Xi'an. This winter, Tom came to Guangzhou to see Mike. They were very happy to see each other. They asked a lot about each other's family and work. They talked about the weather in their cities, too. Guangzhou is quite warm in winter. It doesn't snow in winter in Guangzhou. Some people in Guangzhou have never seen snow. In Xi'an, it often snows in winter. Children like to play snowball fight and make snowmen. That is great fun. Mike hoped to visit Xi'an next winter.