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B
    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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假设你在运动会上百米赛跑成绩是14s，整个过程可分为3个阶段．第一阶段前进14m，平均速度是7m/s；第二阶段用时9s，平均速度8m/s．请估算一下第三阶段的平均速度约是（   ）

某白色粉末由两种物质组成，为鉴别其成分进行如下实验：

①取少量样品加入足量水仍有部分固体未溶解：再加入足量稀盐酸，有气泡产生，固体全部溶解；

②取少量样品加入足量稀硫酸有气泡产生，震荡后仍有固体存在．

该白色粉末可能为（   ）

My mother encouraged me ____ (enter) the competition of this year.

“种瓜得瓜，种豆得豆”，说明了生物界普遍存在____的现象。