Ladies and gentlemen, I returned to this year in a time machine. In the year 2500, we are able to travel through time to any year in the history of the earth. This year is your last chance to change your lifestyle to save the earth.

    Beginning in the middle of the 20th century, a few people were worried about polluting the earth's water and air, but most people did not change their way of life.  Instead, they continued to pour(倒) dangerous chemicals and other waste into lakes and seas, to drive more and more cars and trucks, and to cut down trees.

By the year 2200, the earth's water was completely polluted. Scientists said that in the future there might be too many people on the earth. People could no longer drink water, and they had to use other types of liquids(液体).

So, by the year 2300, there were so many people that food became scarce. There was no water to grow food and all of the fish in the lakes and seas died because of pollution Terrier wars(战争) broke out between the rich and the poor. Scientists were working very hard to find another planet in space where humans could live on.

By the year 2400, the air was too polluted for humans to breathe. So we had to leave earth but only the rich were able to leave. Where did we go? Nowhere. And everywhere. You see scientists did not find another safe planet, so now we must travel around the universe in our space ships. We are still looking for a place to call our home.

    So, it is up to you to change history. There is still hope. You must change your lifestyle now, before it is too late.

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.

    Waste can be seen everywhere in the school. Some students ask for more food than they can finish and others often forget to turn off the lights when they leave the classroom. They say they can afford these things. But I don't agree with them.

    Waste can bring a lot of problems. Although China is rich in some resources, we are short of others, such as fresh water. It is reported that we will have no coal or oil to use in 100 years. Think about it. I think we should say no to the students who waste things every day. Everybody should stop wasting as soon as possible.

    In our everyday life, we can do many things to prevent waste from happening. For example, turn off the water taps when we finish washing, turn off the lights when we leave the classroom and try not to order more food than we need. Little by little, everything will be changed. Waste can be stopped one day if we do our best to form the habit of saving.

    Almost every Chinese can recite the famous poem, "Every grain on the plate comes from hard work(谁知盘中餐, 粒粒皆辛苦)."But sadly, many of us don't actually get the real meaning of these lines：Don't waste food.

    A CCTV programme, News One Plus One, reported that the food Chinese people throw away every year is enough to feed 200 million people for a year.

    Do we have too much food? No, according to the UN World Food Programme, there were 925 million hungry people around the world in 2010, especially in developing countries.6 million children die of hunger every year.

    Chinese people are well-known for being generous. Many even feel that they will lose face if their guests have eaten all the food on the table.

    Luckily, a number of people have realized the importance of saving food. In November, 2011, Li Hong, a waitress in a restaurant in Nanjing, became famous because she took some leftover(剩余的)food home for her son. Many people stood by her side and agreed that it was not right to waste food.

    What should we do in our daily lives to save food? Here are some tips：

    Do not order too much in a restaurant. Only order what you want to eat. If you cannot eat all the food you ordered, take the rest of it home.

    Don't be too picky(挑剔的)about food. Some food may not taste great, but your body needs it.

    Keep an eye on what food you have at home. Don't buy too much, especially vegetables and fruit.