I was only nine years old when I learnt how to use a computer．My mother is my first teacher．I know how to type，how to copy a file，and how to visit a website on the Internet．One day，mom was not at home．I turned on the computer and began to learn how to chat on net．The first one I met there was a boy called Tom．He greeted me politely．When he knew that I was only a 9-year-old girl and almost knew nothing about chatting on net，he started showing me how to use the chatting tools，how to download，and how to send e-mails．I learnt a lot from him．

根据收集到的数据，绘制成如图的统计图（不完整）：

根据图中提供的信息得出“跳绳”部分学生共有____人．

把Rt△ABC各边的长度都扩大3倍得Rt△A′B′C′，那么锐角A、A′的余弦值的关系为（　　）

“螳螂捕蝉，黄雀在后”，这成语从食物链的角度看，缺少的成分是（　　）

我能写漂亮

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