这些是以前的作业:
http://hiphotos.baidu.com/____luan%D8%B7/pic/item/98f7321cc2175687af6e7543.jpg
http://hiphotos.baidu.com/____luan%D8%B7/pic/item/bc6b52b0b62043a630add1a2.jpg
http://hiphotos.baidu.com/____luan%D8%B7/pic/item/98f7321cc2175687af6e7543.jpg
http://hiphotos.baidu.com/____luan%D8%B7/pic/item/bc6b52b0b62043a630add1a2.jpg