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    In today's world, sleep experts say that for a better night's rest, Americans should turn off their smartphones or iPad before sleeping. Such electronic products make the brain more active, and then influence their sleep. But according to a latest survey, more than 90% of Americans regularly use a computer or some other kinds of electronic products in the hour before bed.

    Researchers are finding that man-made light from some electronic products at night may reduce the brain chemicals(化学物质) that help sleep. The researchers showed that sitting in the light from computer tablets clearly lowered levels of the chemical which manages our body clocks and plays a role in the sleep cycle.

    In the study, the researchers let volunteers read, play games and watch movies on a tablet for different time while measuring(测量) how much light their eyes received. They found that two hours of sitting before a bright tablet screen at night reduced the sleep chemical levels by about 22%.

    Studies of students using computers at night have got the similar results. And researchers say that may not only cause sleeplessness, but also raise the risk of obesity(肥胖症), diabetes(糖尿病) and other diseases.

    To be on the safe side, the researchers advise us to use computers less before bed, or at the very least turning down your screen as much as possible.

    You're thirsty and you get yourself a glass of water. Do you ever1how old that water really is? The glass of water that you're2may have fallen from the sky as rain only last week. However, water itself has been around pretty much as3as the earth has! In fact, 4oceans, seas and rivers cover 70％of the earth, there is a 5 supply(供给)of water, which keeps on moving round the earth. This is6of what's known as the water cycle. The sun heats up water and it turns into clouds, which are7from water vapor(水蒸气).When the clouds become8, the water falls back onto the earth as rain. Of course, clean water is absolutely essential for good health. The amount of safe drinking water has gone up around the world, but9one billion humans are still in great need10clean, drinkable water.

    Fire can help people in many ways. But it can also be very harmful.

Fire can keep your house 1, give light and cook food. But fire can burn things 2 . Big fire can burn trees, houses, animals and people.

    Nobody knows how people began to use fire.  But there are 3interesting old stories about how a man or a woman started a fire. One is4 a man. The man 5 a very long time ago. He went up to the Sun and 6 fire down.

    Today people know how to make a fire with matches(火柴). Children sometimes 7 to play with them. But matches can be very dangerous. One match can burn a piece of paper, and 8 it can burn a house. A small fire can turn into a big fire very quickly. So you   9 be careful with matches.

    Be careful with fire, and it will 10 you. But if you aren't careful with fire, it may hurt you.

    Can you imagine that we could build a beautiful city with rubbish? Maybe you will think it is1. However, it can be true! Nothing is a waste if we have a creative mind. Let me show you something about2rubbish.

    Sometimes we can see tons of rubbish in the streets, on the roads, near the buildings... here and there. Many large cities became so ugly3it. Nobody likes rubbish, but in fact, some rubbish can be used again. All of us want to solve the problem, we must do something to4rubbish. We should take action from now on.5, some good things will not be wasted.

    Do you often throw away things you don't need any more? Have you ever thought about how these things can actually be put to good use? For Example, when a car gets too old, it may not run any more. But we can use the metal of the car to make something else. When a bottle is empty, it6as waste. You don't know bottle glass can be made into sand and used to build streets. Rubbish7food can be changed into fertilizer to make plants grow better. It is cheap and safe. And other rubbish can also be used to make building blocks. Now,8machines are designed for that.

    9, people will watch films in a beautiful cinema which is built out of rubbish. Besides buildings and roads, cities may be made from rubbish. But so far, building beautiful cities made from rubbish is only10.

    A famous designer(设计师) and a university student produce a new cup called Vessyl. They have spent several years1it. The smart cup can not only tell Coca Cola from Pepsi Cola,2also tell people whether they should drink water or not.

    When people3liquid(液体) into this smart cup, a few seconds(秒) later, it can check this kind of liquid and tell them what it is. Then it gives4information of the drink, such as sugar, fat and calorie. When people put the cup in their5, it can also show them the condition of their bodies. If they are6, I can tell them to drink water.

    "My partner and I want people to7healthy. In modern society, people are usually8busy to do exercise, or even drink enough water every day. They have much9. We produce this smart cup so that people can make a choice10," the designer said.

    Global warming means the temperature of the Earth is getting higher and higher. If the Earth gets 1, some of the following things could happen:

    The sea level could 2 because of the melting of sea ice.

    Many animals that live on the ice might 3 out.

    There could be more floods(洪水), 4 near the sea and rivers.

    Some plants and animals might die because they cannot live in high 5.

    Global warming is a very 6 problem now. There is something we can do to help to slow it down.

    Scientists have been studying global warming for years. They have found that some things that people do in everyday life make much gas that 7 global warming. One big cause of this is the burning of oil, gas and coal for energy for our cars and homes. This gives off too much greenhouse gas. We can do something to cut 8 on the amount of greenhouse gas.

    ⒈ We can really help by using less energy in life, and less gas in our family cars. We should turn off the 9 and turn down other electrical equipment. We should walk more and use cars less.

    ⒉ 10 can take in some of the greenhouse gas. So we should plant more trees.