C

    If you go into the forest with your friends, stay with them. If you don't, you may get lost. If you get lost, this is what you should do. Sit down and stay where you are. Don't try to find your friends—let them find you. You can help them find you by staying in one place. There is another way to help your friends or other people to find you. You can shout or whistle (吹口哨) three times. Stop. Then shout or whistle three times again. Any signal (信号) given three times is a call for help.

    Keep up shouting or whistling. Always three times together. When people hear you, they will know that you are not just making a noise for fun. They will let you know that they have heard your signal. They will give you two shouts or two whistles. When a signal is given twice. it is an answer to a call for help.

    If you don't think that you will get help before night comes, try to make a little house with branches (树枝). Make yourself a bed with leaves and grass.

    When you need some water, you have to leave your little house to look for it. Don't just   walk away. Pick off small branches and drop (扔下) them when you walk to go back again easily. When you are lost, the most important thing to do is to stay in one place.

    Teenagers are known for being creative and full of new ideas. Let's have a look at these teenage inventions that might change the world.

    Artificial intelligence(AI)(人工智能)is the ability of a computer program or a machine. The computer or the machine with AI can think and learn. It is also a field of study that tries to make computers "smart". John McCarthy, a scientist, came up with(提出)the name "artificial intelligence" over 60 years ago. Many things such as learning and problem solving can be done by computers, though not in the same way as people do.

    An unusual goal of AI research is to create computer programs. They can learn, solve problems, and think logically(逻辑地). At present, Al can successfully understanding human speech, recognizie (识别)human faces, operate self-driving cars and compete in some game systems like playing Chess. However, Some people also consider(认为）AI a danger to humans if it develops too quickly. A famous British scientist also was not for this kind of technology.

    Math is the basic language of AI. If students are good at math, they will be more likely to become successful AI designers(设计者)in the future. We need not only bright students, but also average(普通的)students. As for(对于)average students ，if they get enough math skills, they can also become successful AI designers. Besides, a good knowledge of computer science is also necessary for AI designing.

    Scientists hope to create creative(有创造力)and emotional (有感情的)AI. The AI can possibly understand human feelings or create art. Many ways and tools have been tried to discover this wide and exciting field.

    There are some easy things you can do to protect the environment and the earth. Choose ideas from the list or come up with a few of your own.

    •Plant flowers, grass or trees.

    •Whenever you visit a park or beach, take away what you bring there—keep rubbish in a bag until you can put it in a dustbin.

    •Turn off the lights and TV sets when you leave the room. This can save a lot of electricity.

    •Turn off the tap when you brush your teeth. You can save some water by not letting it run. Also, use a glass cup instead of a paper cup because this saves paper.

    •Keep the doors and windows closed in winter to keep warm air in.

    •Give your old books and magazines to a library instead of throwing them away.

    •Give your old clothes to poor children you know instead of throwing them away.

    •Use both sides of paper.

    •Stop pouring dirty water into the rivers or lakes nearby.

    •Encourage all your friends to do the same things you do to help protect the earth. You don't have to wait until Earth Day to do these things. Make every day Earth Day. If everyone makes a contribution to protecting the environment, the world will become much more beautiful.

    Technology is everywhere. In fact, almost all of us carry a certain piece of technology with us every time we leave the house. What I always forget, though, is just how useful and powerful technology can be when we want to help others.

    There is not a single room in my house that does not have some electronic devices(设备).Whenever I am at home, I am almost always using at least one electronic device. If you walk into my living room on any given day, you will find that, first, I have the television on. At the same time, I usually have my laptop resting on my knee, or I am using my mobile phone. Even when I'm not at home, I am always using my phone, and at work or in cafes, I sit down and connect to the local wireless network on my laptop.

    I must say that I waste a lot of time on the computer and the time I spend on it could be much better spent if I were to take up a little online volunteering.

    Recently I discovered just how much online volunteering there is to do in the world. From using your language skills to do translations, to developing and managing projects and helping with IT work, there is so much that so many people can do to help people in their own countries and across the world. The United Nations, in fact, has a huge page with "Volunteers Recruited" on its website.

    This work can support the poor and help charities who cannot pay for staff members. Many organizations only require you to work an hour a week, some even less. And the support provided by online volunteers can really help make a difference to those in need.

    Scientists think that there has been life on earth for millions of years. However, we haven't found life on other planets yet. The earth is a planet and it goes around the sun. And there are seven other planets that also go around the sun. The sun and its planets are called the solar system. The solar system is a small part of the universe.

    Scientists have launched many spaceships to explore other planets in the solar system. Some spaceships have gone beyond the solar system. However, no one has discovered any life in space yet.

    Why has no one from other planets sent us a message? Have they tried to send information to us? With so many stars in space, are we alone, or is there life on other planets in space?