题干

下列实验现象描述正确的是(   )

A:向锌粒中滴加足量稀硫酸:银白色固体表面出现气泡、固体减少至消失、放热

B:镁在空气中燃烧:发出强光,放出热量,产生大量的白雾

C:向硫酸铜溶液中加入铁钉:紫红色固体表面覆盖一层白色物质,溶液变成浅绿色

D:在空气中点燃一氧化碳:产生明亮的蓝紫色火焰,放出热量

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答案(点此获取答案解析)

A

同类题3

阅读下文,回答问题

    我离教室越来越近。传达室的挂钟告诉我,我竟迟到了30分钟!每走近一步,我的心就跳得格外剧烈。“谁叫你起得这么晚呢?你看还有十分钟,第一节课就要下了!”我暗暗责备自己,并且担心老师严厉地批评我,同学们又会投来责备的眼光……

    走到教室门口,我更慌张了。是进,还是退?我犹豫不决。但是,我忽然想到,在这关键时刻,后退一步,就是容忍自己的错误,就是向自己的弱点退让;前进一步,就是克服缺点的开始,就能多听一分钟的文化知识。想到这里,我毅然地抬脚跨进教室。

    教室里,同学们正在_______地听老师讲课。“报告!”我才喊出口,几十双眼睛“刷”地一下盯在我身上,我赶快低下头,只感到脸上阵阵发烫。这时__老师走过来__严肃又亲切地询问我__李文同学__你今天怎么来得这么迟__我_______地回答:“我……我……昨晚看电视看得太晚了,今天早上睡过了头。”我的头更低了。老师看出了我的心思,亲切地看着我坐下,诚恳地说:“珍惜这短短的几分钟吧!”我偷偷地看了一下周围,同学们的目光是和善的……

    亲切的教诲,善意的目光,使我忐忑不安的心渐渐平静下来。我暗下决心,要把损失的时间补回来。我坐好后,迅速拿出书和笔记本,用自己的纸和笔,带着悔恨和决心,认真地记下了这宝贵的几分钟学到的知识。

同类题5

根据短文内容,从短文后的选项中选出能填入空白处的最佳选项。选项中有两项为多余选项。

Guide for Teenagers

    The teenage years can be tough,and it's normal to feel sad every now and then. But if these feelings don't go away or become so intense that you can't handle them,you may be suffering from depression. ____

Try not to isolate yourself

    When you're depressed,you may not feel like seeing anybody or doing anything. Just getting out of bed in the morning can be difficult,but isolating yourself only makes depression even worse.____.Spend time with friends,especially those who are active.

Keep your body healthy

    Making healthy lifestyle choices can do wonders for your moods. Ever heard of “Runners High”?Physical activity can be as effective as medications for depression,so get involved in sports,ride your bike,or take a dance class. Any activity helps!____.As for food,make sure you're feeding your mind with plenty of fruits,vegetables,and whole grains.

Avoid alcohol and drugs

    You maybe try drinking or use drugs in an effort to escape from your feelings and get a “mood boost”,even if just for a short time. However,substance abuse can not only make depression worse,but can cause you to become more depressed.____.You will need special treatment for your substance abuse problem.

____

    Stress and worry can lead to depression. Talk to a teacher if exams or classes seem overwhelming. In addition,if you have a health concern you feel you can't talk to your parents about,see a doctor. A health professional can help you approach your parents and guide you toward appropriate treatment. If you're dealing with relationships,friendships,or family problems,talk to an adult you trust.

A.Ask for help if you are stressed

B.Even a short walk can be beneficial

C.Turn to your parents for help

D.As you get out into the world,you may find yourself feeling better

E.In short,drinking and taking drugs will make you feel worse—not better—in the long run

F.The more exercise you do,the healthier you will be

G.Help is available and you have more power than you think