求下列各式的相反数与绝对值．

2.5，﹣$\sqrt{7}$，﹣$\frac{\mathrm{\pi }}{2}$，$\sqrt{3}-2$，0．

小林查阅资料获得有关物质燃烧的新信息：

甲.2Na+Cl₂2NaCl                乙.2Mg+CO₂2MgO+C

并形成以下几点认识：

①反应乙属于置换反应      

②工业上常用反应甲生产食盐

③燃烧不一定要有氧气参与  

④使用CO₂灭火应有所选择

其中正确的是（　　）

修改：在错的词下划一横线，并在该词下面写出修改后的词。

注意：1）每处错误及其修改均仅限一词；

      2）只允许修改10处，多者（从第11处起）不计分。

    My mother is a teacher work in a key high school. She is too busy that she often has to get up early and stay up late. In addition to this, she hardly has any times to take exercise. She has been on poor health for some time. My father and I are worried that she may fall ill if she works too hard. These days I'm thinking why to develop my mother's interest in playing sports. Considered that today is Mother's Day, I decided buy a pair of jogging shoes for her. I secret put them on the desk in her study. When my mother entered into her study this evening, she looked surprised, but she immediately realized my intention. She promises that she would go jogging every evening.

克隆羊“多莉”与提供细胞核的母羊长得最像，那是因为（　　）