Have you ever rubbed your hands together when they get cold? Why do we do that? We do that for friction. Friction happens when two things that aren't very smooth rub together to make heat energy. The faster you rub two things together, the more friction (and heat) you can make. Let's discover friction!

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We've all heard of mermaids. They are the beautiful half-human, half-fish creatures(生物). They have the head and body of a human and the tail of a fish. We also know that mermaids only exist in fairy tales. But where did all the stories about these creatures come from? If you have ever seen a manatee, then you might have an idea.
Manatees, which are also called sea cows, are mammals(哺乳动物) that live in the sea. Since they are mammals, they have to swim up to the surface to breathe air. Many people believe that the story of the mermaid began with the ancient sailors who saw the manatees putting their heads out of the water to breathe. Because manatees are upright when they do this, it looks like they are standing. If a sailor saw a manatee doing this from far away across the sea, it is possible that the sailor would mistake the manatee for a creature that is half-human, half-fish.
Mermaids are described as having very long hair. This is probably because manatees like to swim up to the surface of the water in areas where there is sea grass. Manatees eat all kinds of plants in the sea, including sea grass. The sea grass around the manatee's head when they eat could create a picture of long hair.

Manatees also have powerful tails that are very similar to the fish-like tail of a mermaid. The sailors probably watched manatees come up for air and then swim back below the surface, using their paddle-shaped tails. This would explain why the sailors thought mermaids had fish-like tails.

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    Google and Toyota have worked together to create a new smart car. It can run on the road without a driver. It drives itself. The self-driving car hasn't been on sale to the public, so we don't know how much it costs. Another thing most people want to know is whether it will be safe enough to run on the road.

The self-driving car uses electricity (电) as its power, and it can't drive very quickly—the top speed would be 25 miles per hour. It is actually controlled by a computer system on the car. The system keeps on collecting information by some video cameras inside the car and a LIDAR sensor(激光达传器) on top of it. A computer processes the information and decides what to do. "The self'-driving car has only buttons (按钮) for go and stop, so it's very easy to use," an engineer of Google says. "And what's more, it will make car accidents fewer and make the world a safer place." The self-driving car has driven hundreds of thousands of miles in California, and it has only gotten into two accidents by human mistake.

    According to CNN, self-driving cars will also help to reduce the number of cars in big cities. "Self'-driving cars would be able to send you to the workplace and then pick up another person instead of stopping in a parking lot."

    Rainforests (热带雨林) cover six percent of the earth's surface (表面). There are rainforests in many parts of the world. About 75 percent of animals live in rainforests. There are many beautiful birds, insects and so on. Some of them live on the ground, some live under the ground and others live in the trees, over 30 meters from the ground. It is always hot in the rainforests and the ground is always wet. It is also very dark there.

    The rainforests are very important for us. We need them! The trees and other plants in the forest help to make the air clean. They also help to control (控制) the temperature.

    Unfortunately, in many places, the rainforests are in danger. For example, many years ago there was a large rainforest in Java, but now there is nothing. The same thing happens now in many other parts of the world. It's time to take action to save the rainforests. We can never imagine a world without rainforests. If rainforests disappeared from the earth, we wouldn't find any trees, flowers or fruits. What's more, we wouldn't get clean air, and we wouldn't find any animals. The worst result would be that we wouldn't find any humans.

    Thousands of years ago, people couldn't live for long. Most people only lived to be twenty-five or thirty years old. 20% of people died before they were twelvemonths old and another 30% could not live to be five years old.

    Today, people can live much longer. One reason is that the water we drink is cleaner. Clean water does not cause diseases（疾病）. Besides, medical treatment is better today. More and more people live to be over eighty.

    Women often live longer than men. For example, in Japan, women usually can live to be eighty-five, but men can only live to be eighty.

    In the future, people will probably live longer than today. Here are many things we can do to help people live longer. For example, we can make sure that everyone has enough medicine to fight against diseases. Also, it is necessary for everyone to have enough to eat. Today many people die because they do not have enough food.