A smile will tell people around you that you are a kind and friendly person. However,many people don't smile because they think they ugly teeth. For example, one of my classmates, Mile, doesn't have very nice teeth,so thatis why he seldom opens his mouth.he even says that he has lost cofidence because of his teeth.So it is very important for us to look after our teeth. In fact, a lot of people have this problem. Some people inherit teeth problems from their parents,while others'teeth are damaged because of bad habits,like heavy smoking,eating too much sugar or not brush-ing teeth often.If your teeth are in bad shape, you should see a dentist and ask for help. They can help improve your teeth and tell you how to take care of then.
   Smiling can help you to feel more confident and make other people think of you as a more friendly person. If you want to keephealthy, you should not only smile but also laugh. An Indian doctor called Kataria said that young children should laugh about 300 times a day, wile adults should laugh between 7 and 15 times a day. So please take this chance to smile and laugh now!

    The world is not hungry, but it is thirsty. It seems strange that nearly 3/4 of the Earth is covered with water while we say we are short of（短缺）water. Why? Because about 97% of water on the Earth is sea water which we can't drink or use for watering plants directly(直接地）. Man can only drink and use the 3%-the water that comes from rivers and lakes. And we can't even use all of that, because some of it has been polluted(污染）.

    Now more water is needed. The problem is Can we avoid（避免）a serious water shortage later on? First, we should all learn how to save water. Secondly, we should find out the ways to reuse it. Scientists have always been researching in the field. Today, in most large cities water is used only once and then runs to the seas or rivers. But it can be used again. Even if(即使）every large city reused its water, there would not be enough. What can people turn to next?

    The seas seem to have the best answer. There is a lot of water in the seas. All that needs to be done is get the salt out of the sea water. This is expensive, but it's already used in many parts of the world. Scientists are trying to find a cheaper way of doing it. So you see, if we can find a way out, we'll be in no danger of drying up.

    Now, it seems that artficial intelligence （人工智能）is becoming more and more popular in our life, and it has greatly influenced the ways we live, work and play. Can you imagine that you can play table tennis with a robot one day?

    Recently, a scientist has invented a special robot that can be a table tennis coach. That means people can practice table tennis not only with humans but also with a robot.

    Named Forpheus, the smart table tennis robot is quite special. It can study the movements of human players and the speeds of the ball. In this way, it can exactly judge (判断) the player' skill levels (水平). Then it uses the information to change the ways to play. If the player are just beginners, Forpheus will play in a slow and easy way, but if the players are better ones, the robot will play in a faster and more difficult way. What's more, while playing, it encourages players to try their beat with words like "Good job!", "Come on!" and so on. At the same time, it gives some good advice to improve their skills. So it is both a good partner and a clever coach.

    Science and technology is developing quickly these days and it's hard to imagine what will happen in the future. "In the next 20 years, it will be possible that one robot teaches another to play table tennis or even invents another one!" Takuoya, the inventor of the robot, said.

    Fresh green grass, Hundreds of colorful wild flowers. Water running into little pools. Birds making their homes in boxes. The 9, 500-square-metre Augustenborg Botanical Garden may look just like any other well-organized park but there's a difference. It lies on the roofs (屋顶) of industrial and office buildings in the city of Malmo in Sweden.

    Green roofs are not a new invention. And now they are getting popular again. The common roofs of a modern city have endless black surfaces with no life or water. Perhaps that's why a garden on a roof becomes such a perfect choice for more and more people.

    Green roofs are not just pretty. They also help to moderate the city temperature. The high temperatures on common roofs in the summer can make top floor flats uncomfortably hot. What is more, they play a part in making the cities hotter than the countryside around them, causing the "urban heat-island effect". On a green roof, however, with its plants and water, temperatures change only a little, as they do in a park. This can greatly cut the costs of heating and cooling in the building below.

    Also, a green roof takes in rain water, and protects the city drainage (排水) system.   ▲    And small animals and birds can make their homes on it. Thanks to this, the city may become part of nature, rather than something completely separate from it.

    While the cost of building such a roof can still be higher, it can be cheaper in the long term as a result of energy savings. And wouldn't it be wonderful to be able to walk out into a garden high above the city's noise and traffic, whether you're at school or in an office or just at home in a ten-floor block?