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.

16世纪初到19世纪中叶，中国逐渐在社会前进的竞赛中输给了西方。阅读下列材料，回答问题。

材料一：明朝的政权和皇帝的权力，在中国历朝中是最为绝对的。明太祖废除宰相以后，皇帝直接管理政务……特务机构锦衣卫、东厂，随时可以逮捕、拘禁、处死官吏与百姓……朱元璋恢复科举制度时，规定读书人只能读“四书”……因此，这个政权可说是中国历史上前所未见的专横暴力。

材料二：

分解因式：a³﹣9a=____．