题干

某动物的肤色受两对势位基因A、a和B、b控制(两对基因独立遗传).当不存在显性基因时,肤色为白色;当存在显性基因时,肤色为黑色,而且显性基因数量的增加,黑色会逐渐加深(A和B的遗传效应相同).现将两只肤色相同的纯合子作为亲本杂交得F1,F1雌雄个体自由交配得F2,F2中肤色有白色个体和4种不同深浅的黑色个体.

(注:该种动物一胎可以生产多只子代,肤色遗传与性别无关.)

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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