下图漫画说明生命科学面临的难题是(　　)

    Happiness is important for everyone. Most people want to be happy, but few know how to find happiness. Money and success alone do not bring lasting happiness. Happiness depends on ourselves. In other words, we make our own happiness. Here are a few ways to help you be happier.
    The first secret of happiness is to enjoy the simple things in life. Too often, we spend so much time thinking about the future—for example, getting into college or getting a good job-that we fail to enjoy the present. You should enjoy life's simple pleasures, such as reading a good book, listening to your favorite music, or spending time with close friends. People who have several close friends tend(有……打算) to live happier and healthier lives.
    The second secret to leading a happy life is to be active. Many people experience this, dancing or playing a sport. You can forget about your problems, and only think about the activity.
    Finally, many people find happiness in helping others. According to studies, people feel good when they volunteer their time to do many meaningful things for other people. If you want to feel happier, do something nice for someone.
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现实生活中，我们会遇到各种各样的“标志线”。下列属于关爱公民生命健康权的“标志线”是（）
①横穿马路的“斑马线” ②施工现场的“警戒线”  ③银行窗口的“l米线” ④火车站台的“候车线”