Do you like drinking coke, coffee, juice or milk? Do you often drink them instead of water? However, of all the things we eat and drink, water is the most important. Not all of us understand this but it is quite true. Human body can go without food for a long time, but two or three days without water usually makes people die.

    Many people do not understand how much water the human body needs to work well. What is true is that many people do not drink enough, especially in hot weather. Most people drink only when they are thirsty but often need more water after they take exercise.

    Does anyone know what is the 65%-75% of human body? It is water. If we do not have enough water, we will feel tired and become ill. So, do you know what the best drink is? It's water.

    Computer are very popular now .People are talking about and using the Internet everywhere, but how many of us know the history of the Internet?

    Many people are surprised when they find out that the Internet was set up in 1960s. At that time, Computers were large and expensive. Computer networks didn't work very well. If one computer in the network broke down, then the whole network stopped. A new network system had to designed. It should be good enough to be used by many different computers. If part of the network was not working, information could be sent through another part. In this way, the computer network system would keep working well all the time.

    At first, the Internet was only used by few people, but in the 1970s,it was used in school, hospitals and banks. However, computers were still expensive and the Internet was difficult to use. At the beginning of the 1990s, computers became cheaper and easier to use.

    Today it's easy to get online and it is said that millions of people use the Internet every day. Sending e-mails is more and more popular among students. The Internet has now become one of the most important parts of people's life.

    Many families make some house rules to make sure that everyone has a safe and happy home environment when they're home alone. Different families have different rules，but here are some rules many families follow：

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    Keep your house keys hidden inside a pocket.

    Don't lend your keys to others.

    Hiding a key under a rock or a flowerpot isn't a good idea.

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    Don't open the door to anyone except a sibling（兄弟姐妹）or parent.

    Keep all doors locked at all times.

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    Most families have a rule that no friends are allowed in the house when someone's at home alone. This may be no fun but in the end，it is safer for everyone.

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    Your parents may want you to stay at home and go nowhere-not even a friend's house，the park，or the store.

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    Many parents ask their kids to wait until a parent is home before going online.

    These may sound pretty strict，but you'll be surprised how they help you feel safe！

    Most of us probably dreamed about becoming an astronaut when we were little. But how many of us have actually become one, or are at least working toward it? It's true that the advice" Always follow your dreams" is something that is typically easier said than done.

    But still, this is the one piece of advice that Alyssa Carson wants to share with her peers. This 17-year-old girl from the US has become one of the candidates (候选人) for NASA's 2033 project to go to Mars. If everything goes well, Carson will be one of the first human beings to ever set foot on the red planet.

    Carson began to dream of going to Mars when she was only three years old. After watching an astronaut-themed cartoon and hearing from her father that humans had only been to the moon but not Mars, Carson decided that she wanted to be the first one to do so.

    To realize her dream, she has worked hard toward it. At the age of 12, Carson became the first person to attend all three NASA space camps, and she sat with real astronauts to discuss the future of Mars missions. Now 17, Carson is continuing with her space training while still taking on her high school work like a "normal " teenager, except that she studies all her subjects in four languages - English, French, Spanish and Chinese.

    "I don't think there's anything specific that makes it easier for me or makes it something that others can't do," Carson said in an interview," I've just really focused myself on what I want to accomplish."

    Besides, Carson is willing to make sacrifices (牺性) for her dream, She's fully aware of the danger of the mission and the possibility that she might never be able to come back. She also accepts the fact that she can't get married and start a family because any loved ones left on Earth may be a distraction for her and for the mission, But Carson believes that it's all worth it, summarizing her view with this ancient Greek proverb she once quoted," A society grows great when old men plant trees whose shade they know they'll never sit in."

    While some people's dreams may sound out of this world, Carson is on her way.