Plants are very important living things. Life could not go on if there were no plants. This is because plants can make food from air, water and sunlight. Animals and men can't make food from air, water and sunlight. Animals get their food by eating plants and other animals. Therefore, animals and men need plants in order to live. This is the reason why we find so many plants around us.

    If you look carefully at the plants around you, you will find that there are many kinds of plants. Some plants are large while others are small. Most plants are green.

    Some plants have many small leaves. Others have only a few. There are many kinds of leaves. Leaves are of different shapes and colors.

    Leaves are also different in other ways. Some leaves have long thin parts at the end, we call them leaf stalks, some have short leaf stalks, others even have no leaf stalks. The leaf edges are also different. Some leaves have smooth(平滑) edges. Some have a wave-shaped edges. Others have edges like the teeth of a saw(锯子).

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    Hippos(河马) live in Africa(非洲). They are one of the world's largest land animals. Here are some interesting facts about them.

●Where are hippos born?

    Hippos often give birth in the water. The hippo babies get out of water right after birth to take their first breath.

●How quickly do hippos grow up?

    Hippo babies nurse both under water and on land for a year. Then they stop taking their mothers' milk but they are still with their mothers until they are eight years old. Then they move out.

●What do hippos love?

    Hippos love water and they spend most of the day in it to stay cool. The Hippo can breathe, see and hear when its body is under water because its nose, eyes and ears are on the top of its head.

●Do hippos swim better than people?

    Yes, they are great swimmers and they can hold(屏住) their breath for five minutes. Hippos can even walk under water along the bottom(水底) of rivers and lakes.

    In earliest times, men considered lightning to be one of the great mysteries (神秘的事物) of nature. Some ancient peoples believed that lightning and thunder were the weapons (武器) of the gods.

    In reality, lightning is a flow of electricity formed high above the earth. A single flash of lightning 1.6 kilometres long has enough electricity to light one million light bulbs (灯泡).

    The American scientist and statesman, Benjamin Franklin, was the first to show the connection between electricity and lightning in 1752. In the same year he also built the first lightning rod (避雷针). This device (装置物) protects buildings from being damaged by lightning.

    Modern science has discovered that one stroke (闪击) of lightning has a voltage (电压) of more than 15 million volts (伏特). A flash of lightning between a cloud and the earth may be as long as 13 kilometers, and travel at a speed of 30 million meters per second.

    Scientists judge that there are about 2,000 million flashes of lightning per year. Lightning hits the Empire State Building in New York City 30 to 48 times a year. In the United States alone it kills an average (平均数) of one person every day.

    The safest place to be in case of an electrical storm is in a closed car. Outside, one should go to low ground and not get under trees. Also, one should stay out of water and away from metal fences. Inside a house, people should avoid open doorways and windows and not touch wires or metal things.

    With lightning, it is better to be safe than sorry?

    What's a spacewalk? Any time an astronaut gets out of a spacecraft(航天器) while in space, it is called a spacewalk. Astronauts go on spacewalks for many reasons. For example, experiments can be placed on the outside of a spacecraft. This lets scientists learn how being in space affects(影响) different things. By going on spacewalks, astronauts can also fix things instead of bringing them back to the earth to fix.

    When astronauts go on spacewalks, they wear spacesuits to keep themselves safe. Inside spacesuits, astronauts have the oxygen(氧气) they need to breathe and the water they need to drink. To keep the astronauts and the spacecraft safe, the astronauts must leave and go back to the spacecraft through a special door. When on a spacewalk, astronauts use safety  tethers to stay close to their spacecraft. Tethers are like ropes, connect the spacewalkers with the spacecraft. They keep astronauts from floating(漂浮) away into space. Another way astronauts stay safe during spacewalks is by wearing a SAFER. SAFER is worn like a backpack. It helps an astronaut move around in space.

    How do astronauts train for spacewalks? One way is by going for a swim. Floating in space is a lot like floating in water. Astronauts practice spacewalks underwater in a huge special swimming pool. For every one hour they will spend on a spacewalk, astronauts need to train seven hours in the pool. Another way astronauts practice for a spacewalk is by using virtual reality(虚拟现实). It looks and feels just like a spacewalk.

    Today, only three countries have finished spacewalks independently. They are Russia, the United States and China. The first person to go on a spacewalk in the world was Alexei Leonov from Russia. Zhai Zhigang is the first Chinese astronaut to go on a spacewalk. The world record of spacewalks is held by Russian astronaut Anatoly Solovyev. He has been on 16 spacewalks and spent more than 82 hours outside in space.

    Owls live in almost every country in the world. Most owls don't sleep at night. When they fly, you can't hear them. They are very quiet. Owls are good at hunting（捕猎）. They eat a lot of things such as mice, snakes, small birds and even fish. Owls have very good hearing. That helps them to hunt well in dark places. Their eyes are special. Both of their eyes face front. They can see very far away. There are facial disks(面盘) around their eyes. These facial disks can help with their hearing. Owls can turn their heads 270°. That helps them see what's going on all around them.

    Maybe because owls look a little different and have special life habits. There are a lot of stories about them. Some cultures believe that owls are very clever and some cultures think owls may bring bad luck to people. In fact, owls are really good friends of people. They eat lots of mice every year. That helps save a lot of food for people. But the number of owls in the world is becoming smaller and smaller because of people's activities. Now owls are protected by law(法律) in many places of the world. For example, in some places, people can't keep an owl as a pet at home.