对一切实数x，不等式$x^2+a\left|x\right|+1\ge 0$恒成立，则实数a的取值范围是（　　　）

    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．

步骤一：取三支相同的试管编号为1、2、3，各试管内依次加入下列药品

步骤二：将三支试管振荡后，静置，插入热水浴（约75℃）中，加热约5min，加热过程中不再振荡．

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