题干

在数轴上把下列各数表示出来,并用“<”连接各数.﹣|﹣2.5|,1
1
2
,-(-2
1
2
​),﹣(﹣1)100,﹣22.
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答案(点此获取答案解析)

解:这些数分别为﹣2.5,1
1
2
,-(-2
1
2
​),﹣1,﹣4.在数轴

同类题2

阅读短文,回答问题。

生命

    ①生命必定要死亡吗?不,有两个事实可以证明:第一,任何生物的生殖细胞都是永生不死的。它们已经不断分裂,不断生存了几千万年以上,而且还在继续生存下去。没有生殖细胞的永生,也就没有物种的延续。第二,癌细胞不会自动死亡,也是永生的。海拉细胞,这是多年前从一位叫海拉的女子身上收集到的子宫颈癌细胞。它一直在全世界各个实验室里分裂繁殖,每24小时倍增一次,生长分裂极其旺盛,至今已传了上千代,仍没有死亡的征象。海拉早已死亡多年,而她的癌细胞却能永生。这里的奥秘何在呢?

    ②美国细胞学家海弗利克发现,人体细胞从第1次分裂开始算起。毕生只能分裂50次左右,此后便衰老死亡。为什么癌细胞与生殖细胞可无止境地分裂下去?海弗利克认为,这是因为正常体细胞之间紧密联结,闭关自守,缺乏遗传信息的交换,而癌细胞恰恰相反,它能与病毒或其他生命物质发生信息交换,从而使自身生命不息。这也许是永生的奥秘吧。

    ③如果我们将癌细胞或生殖细胞永生的机理弄清楚,并应用于人类,岂不是也可让我们的体细胞获得永生吗?如果体细胞也与外界进行遗传信息交换,是否也可无限期分裂而长生不老呢?有一位细胞学家,利用遗传工程将哺乳动物的神经细胞移植到金鱼卵细胞中(体细胞与生殖细胞结合),促进了遗传信息的交换,使神经细胞分裂了100次尚未衰老,依然生机蓬勃。

同类题4

请认真阅读下面短文,并根据短文内容回答问题。
      Do you feel lonely when your best friend isn't around? Here's our advice to you ---and to all kids who feel lonely sometimes. 
It's hard when a best friend isn't around --- maybe because he or she moved to a different school or a different class. You may feel left out at break or lunchtime. You want to have new friends, but how do you make them? Maybe it seems everybody else already has his or her friends. But remember, there's always room for more friends.
      Start by looking around your classroom --- think about which kids you'd like to play with at break. Look for chances to say hi to them, smile, and be friendly. Offer to share something or express your appreciation (欣赏) to them. Invite someone to play with you or say, “Do you want to sit here?”in the lunchroom. When you're at break, walk over to kids you want to play with, act friendly, and say “Hi, can I play, too?” or just join in. 
     If you have trouble doing this or if you're feeling shy, ask your teacher to help you make new friends. Teachers are usually pretty good at matching up friends. The best way to make friends is to be a friend. Be kind, be friendly, share, say nice things, offer to help ---and pretty soon, you'll have one, or two, or even more new friends.
     You might still miss that special best friend. But when you see each other, you can share something you didn’t have before he or she left. You can introduce him or her to your new friends!
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