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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.

When man began to search the skies, he saw a lot of things. In the universe, the earth seemed to be just a small bit of dust. It is only a small planet, and travels around the sun. The sun together with its planets, travels in the Milky Way（银河）, our galaxy（星系）. The Milky way has about thirty billion stars like our sun, and is one of about a hundred million galaxies in the universe. Because the space is so great, it is difficult to work out how far away a star is. Instead of kilometers, we have light years. A light year means the distance light travels in one year. Our nearest neighbour galaxy is more than 9,000,000 light years away from the earth.

    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.

    We all know that the panda is the treasure (珍宝) of our country. Then how about its droppings (粪便)? They are treasure, too. How?

    The panda keeper1an adult panda with about 25 kilos of bamboo every day. Of that, the panda will eat about 11 kilos — the most2parts. Because the panda cannot digest (消化) all the bamboo completely, its droppings3much of undigested (未消化的) bamboo. Can people make use of it? Sure, someone4in turning it into toilet paper.

    "In my opinion, it's a great5 ， " a panda keeper says. "In the past, we just threw away the droppings6rubbish. But now workers come and take the droppings away. They use the droppings to make7. They also make notebooks and bookmarks. "

    8 ， the paper doesn't sell well at the Panda Base. It is not popular with9. Most of them won't buy it after they visit the Panda Base. "A box of tissues (纸巾) is 43 yuan ， " they said. "That's quite10. " If you see the tissues at the Panda Base, will you buy them?

    My name is Miranda Gibson. I have been at the top of a tree for five months now. Some people might wonder 1 on earth I would choose to do that.

    I have walked 2 this forest many times. On 12 December 2016, machinery (大型机械) rolled into the forest and the destruction (摧毁) began. I couldn't bear (忍受) the thought that these forests would be 3 forever. So, on 14 December 2016, I put my clothes into a bag, 4 my job plans, and climbed 60 meters to the top of this tree. I have been there ever since.

    Life in the tree tops can be challenging. I have times when I feel frustrated (沮丧的) and I wish I could 5 to have a holiday for a few days! There are times too, when I feel terribly 6. I miss my friends and family.

    Living on the tree has been exciting and encouraging. I am willing to 7 up here for a long time, 8 I honestly hope it won't be too 9 before I can put my feet on the ground below and stand in a forest that will never 10.