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!

    Many animals hide to stay alive. They hide in many ways. Some animals hide in leaves; some animals hide in snow. Usually their colors or shapes help protect them. It's hard to see an Arctic bear in snow. Its white fur helps protect it. Chameleons(变色龙) can hide by changing colors. Their skin turns the same color as what is around them. Some chameleons can change colors in five minutes.

    Many animals try to look bigger than they are to stay alive. Some animals can make other animals think they are very big. If they look very big, animals that are looking for food will run away. Bears can walk on two legs. They look very, very scary. Some animals will run away from them.

Many animals try to stay around other animals. This helps them stay alive. Zebras stay close together so that they can help each other look out of danger. Seeing many stripes at once can also confuse animals that want to eat them. Some birds stay in a circle, each toward a different direction. In this way they can also help each other stay alive by looking around for animals that many want to eat one of them.

阅读下列短文，从每题所给的四个选项（A、B、C和D）中选出最佳选项。

    Jogging is good for us and helps us live longer and healthier. It's easy to do and free. You do not have to spend money jogging. You can do it in a park or even in your home. But many people find it boring after jogging for a while. Then how can we keep jogging fun? Here are some ideas to make your jogging more interesting.

    First, you should choose to wear your favourite sports clothes and shoes when you jog. They make you more comfortable and more likely to run.

    Always jog outdoors. By changing your route, you can choose another street, and you will always have something interesting to enjoy when you jog.

Take along with your MP3 player and listen to your favourite songs when you jog. The music can make you excited and run farther without feeling bored.

    It's always more enjoyable with a friend. Make friends while jogging. Join a running club, find a new running partner, or invite an old friend to go jogging. It's better to find a friend who runs a little faster than you. Then you can try to catch up with him or her.

    Building an app is a big project. If you want to build the next great smartphone app, you need a plan. First, think about the kind of app that you want to build. Will your app be a game? Will it be for business? Then make a schedule(日程安排)for building the app. You need plenty of time for research before you are ready to build.

    Now you're ready to make the app. Building an app is like a puzzle(拼图)with many different parts. You can build it yourself or find a company to help you. There are many videos and websites that can teach you to build one. Some websites provide "building blocks" for app developers. As you build, you pick blocks from the website and put them in your app.

    After you build your app, you need to check it carefully. Look for bugs. Most apps have several problems to fix. Show your app to people. Ask their opinions. Mike sure everything works before letting people download it. There are so many tools that can help you build apps. Having the right tools will make the work easier. Now almost anyone can make a new app.

    Thanks to software like Apple's Siri or Microsoft's Cortana, it's easier than ever to do something on our phone or computer. All we have to do is "talk", and our favorite song starts playing a few seconds later. But in the neat" future, asking our phone to play a song by using our voice will seem as old--fashioned. That's because US tech company Microsoft recently applied for a patent* for a "brain control interface"(BCI): meaning that soon, we may be able to control our phone and computer with our thoughts.

    BCI technology works by changing brain signals into computer commands. This technology isn't brand new, however. Last year, for example, it was reported that scientists were able to help a disabled man from the US, 53-year-old Bill Kochevar, to move again. To do this, Kochevar was fitted with BCI technology, as well as equipment to make his muscles move. After a few weeks of getting used to it, Kochevar was able to use his thoughts to "tell" the BCI to move his muscles, meaning he was able to feed himself for the first time in years.

    Apart from helping disabled people, it's hoped that BCI technology will improve the daily lives of other people too. US social networking platform Facebook announced last year that it was working off BCI technology to help people type by using their brain. By 2020, the company hopes to have created a system that will allow people to type up to 100 words per minute just by thinking about them.

    However, many people are worried that technology that tan read our thoughts will create privacy problems, especially if social media companies are included. But Facebook researcher Regina Dugan said at a meeting last year that the company has no interest in reading people's private thoughts. "That might be more than any of us care to "know. And it's not something any of us should have a right to know," she said.

    Big ocean fish have almost been endangered since the start of business fishing in the 1950s. The scientists found that the number of large fish has dropped by 90 percent in the past fifty years. The study took ten years. The researchers collected records from fishing businesses and governments around the world. The magazine Nature published (发表) the findings.

    The scientists say the common way called long line(多钩长线) fishing is especially harmful to large fish. This way includes many fishing lines that are connected (连接) to one boat. If these lines are joined together, they can reach one hundred kilometers. They hold thousands of sharp metal hooks to catch fish. Long line fishing is especially common in the Japanese fishing industry. Records showed that Japanese boats used to catch about ten fish for every one hundred hooks. The study says long line fishing boats now might catch one fish per hundred hooks.

    The scientists say business fishing can destroy groups of fish much faster than in the past. The study suggests that large fish can disappear almost completely from new fishing areas within ten to fifteen years. Ocean life systems could be destroyed.

    It's not the only worry that the number of large fish is becoming smaller and smaller. What's worse, they are smaller in size than their ancestors (祖先).