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    Hello!I'm Kate．I want to talk about my smart phone(智能手机)．My smart phone is white．It's from my uncle Sam．He works in New York and comes back to London every December．I like mv smart phone．It is useful.
    The school rules don't allow(允许)us to take smart phones to school,so I usually use it after school or on the weekend．When I go out with my friends，I like keeping it in my bag．So my family can call me at any time．When I don't go to school．I like to call my friends to talk to them，or ask them for help with my study．I'm not very good at math，so I put an APP(应用软件)about math in my smart phone to help me． It is fun and helpful．I also use the smart phone to do some reading，play games，and watch movies．Isn't it great?
    Sometimes smart phones are not good for people．Some people spend too much time on it．I like my smart phone and I know how to let it help me. It's my good friend．
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实验用的托盘天平的底座做得又大又重，这是用了增加支承面和____ 的方法来使天平稳定，天平使用时要放在水平桌面上，是因为重力方向是____．

下列选项中说法错误的一项是（    ）