题干

下列关于空气的说法中,错误的是(  )


A:工业上利用氧气和氮气的沸点不同,从液态空气中分离出氧气的过程属于物理变化

B:空气是一种十分重要的天然资源

C:若少量有害物质进入空气中,靠大自然的自净能力,大气还能保持洁净

D:按质量分数计,空气中约含有氮气78%、氧气21%、其他气体和杂质1%

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答案(点此获取答案解析)

D

同类题4

阅读下面材料,在空白处填入适当的内容(1个单词)或括号内单词的正确形式。

           We're human, and it's not always easy to get along with everyone all the time.Sometimes we hurt other people's feelings without intending to. Sometimes,we're ____(deliberate) mean and we feel bad afterward. So we apologize. Apologies are one of the tools we use to build good friendships andrelationships. ____ you say“I'm sorry” (and really mean it), it's because youprobably feel bad that something you did or said hurt the other person. Sayingyou're sorry is more than just words. You're also saying that you respect theother person  ____  you care about his or her feelings.Apologizing shows you have empathy.

     After  apologizing,you might feel alittle ____(good).The other personprobably will, too. When you apologize in a caring way, you can feel goodbecause you are trying to make things right again.

     Some times a heartfelt“I'm sorry” ____(fix) everything right away. Other times,it might take  ____while for someone to get past feeling upset. You may need to give the otherperson some time. Even after you say you're sorry, you might still feel bad aboutwhat you said or did—but you can feel good about apologizing, fixing themistake, or making up your ____ to do better. When someone apologizes to you,you may welcome it and be ready to forgive  ____ happened and move on. Or you might not feel like being friendly againright away. If a person keeps hurting you and ____ (apologize)without making aneffort to change,you might not want tohang about ____  that person any more.