节肢动物就是身体由很多体节构成，体表有外骨骼、足和触角分节的无脊椎动物，下列哪组是节肢动物？（　　）

改错题

Dear Editor,

    I am writing tell you about the discussion we've had about whether it is necessary of middle school students to have mobile phones. Most students think this is more convenient for them to keep in the touch with their parents and classmates. And what's much, it's a fashion. However, most teachers think middle school students are not old enough to control them. It is a waste of time for students to play games and sending messages on their mobile phones. Therefore, it is easy to make students contact with each other. In my opinion, following the fashion was understandable. But as middle school student, we should put all our energy into our study.

Yours truly,

Mary

在平面直角坐标系中，点P（1，1），N（2，0），△MNP和△M₁N₁P₁的顶点都在格点上，△MNP与△M₁N₁P₁是关于某一点中心对称，则对称中心的坐标为 ____.

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抗流感药物—“达菲”被认为是迄今为止对禽流感最有疗效的药物后，全球对达菲的市场需求膨胀，达菲的主要原料莽草酸一下子成了抢手货，价格上涨几倍。全球蔓延的H1N1甲型流感，感染早期用达菲（Oseltamivir）有显著效果。“达菲”的原料莽草酸是我国传统的香料——八角茴香的重要成份。请你根据莽草酸的化学式（C₇H₁₀O₅）计算：