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. 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.

     Now more water is needed. The problem is: Can we avoid a serious water shortage (短缺) 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 making studies in the field. Today，in most large cities water is used only once and then runs to the sea or rivers. But it can be used again. Even if every large city reused its water，still there would not be enough. What could people turn to next?

     The sea seems to have the best answer. There is a lot of water in the sea. All that needs to be done is to 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.

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    People know the danger of fires. It's good for a family to learn how to prepare for a fire. Here are some suggestions：

    Put a smoke alarm in the house. Smoke from a fire causes the alarm to go off. The alarm makes a loud sound. The sound tells everyone to leave the house at once.

    Make escape (逃脱) plans. They should know all the ways out of the house. If there is a fire， everyone follows the plan to get out. Part of the plan is to check all the windows to make sure they can be opened easily.

    Buy fire extinguishers (灭火器) in the house. Everyone in the family should know how to use them.

    Practice for a fire. They do fire practice because they teach children about fire safety. Everyone in the family should know the following fire rules：

    ＊Don't open a hot door! The fire can grow more quickly if you open the door.

    ＊Stay close to the floor! Smoke can be more dangerous than fire； the best air is near the floor because smoke rises.

    ＊What will you do if your hair or clothes start to burn? First， stop! Don't run! The fire burns faster because of more air. Drop! Fall to the floor. They roll! Turning over and over will make the fire go out. Put a blanket (毯子) around you to keep air away from the fire that may still be on you.

    There are many possible causes for fires. A wise family is ready all the time. If there is a fire， don't forget to call 119 for help.

    The expression "lanshouxianggu" has been quite popular on Chinese social networking sites. You may have used it many times when chatting online. However, did you know that the "blue thin mushroom" was not just magic of Photoshop and was really there in nature?

    Well, let' s meet Entoloma hochstetteri (霍氏粉褶菌).This is a kind of naturally-blue fungus(真菌) The plant looks very small. Its sten' s diameter(梗的直径) measures only about 5 millimeters. Entoloma hochstetteri can be found widely in New Zealand, especially on the west coast. The Maori name for it is "werewere-kokako." It seems New zealand is very proud of producing this unusual species-the country prints the blue mushroom on its $50 notes.

    Athough the species is very unusual, little is known about it. Silas villas-boas is a scientist at the University of Auckland. He said he was very disappointed that nobody had ever tried to test the blue mushroom in the lab, "You can even count the number of scientific articles on it on one hand, he said. The scientist decided to be the first to study the plant. A group of researchers have been helping him with the study.

    In an early test, the researchers found alkaloids(生物碱) and Omega-3 fatty acids(w-3脂肪酸)in the blue mushroom. While the acids are helpful to health, alkaloids soetimes influence how the brain works. However, Villas-Boas said the substance was very common in plants. So far, the researchers have not found any toxins(毒素) in Entoloma hochstetteri, but they are not yet sure if it can be eaten. Villas-Boas said more testing would be required.

    Have you ever heard someone use the phrase "once in a blue moon"? People use this expression to describe something that they do not do very often. For example, someone might say that he tries to keep away from sweets because they are unhealthy, but will eat chocolate once in a blue moon. Or someone who does not like to. Go to the beach might say, "I visit the shore(岸边) once in a blue moon." While many people use this phrase, not everyone knows the meaning behind it.

    The first thing to know is that the moon itself is never actually blue.  This is just an expression. The phrase "blue moon" actually has to do with the shape of the moon, not the color.

    As the moon travels around the earth, it appears to change shape. We have certain names for certain shapes of the moon. For example, when we can see a small part of the moon, it is called a crescent moon. A crescent is a shape that looks like the tip of a fingernail(指甲). When we can see the moon appear in the sky as a thin crescent, it is called a new moon. When we can see the whole moon, it is called a full moon. Usually, there is only one full moon every month. Sometimes, however, there will be two full moons in one month. When this happens, the second full moon is called a "blue moon".

    It's predicted(预言) that there will only be 15 blue moons over the next 20 years. As you can see, a blue moon is a very unusual event. This fact has led people to use the expression "once in blue moon" to describe other" very unusual events in their lives.