Dreams can happen in any of the four stages of sleep. The most memorable and clearest dreams happen in the last stage of sleep (also known as REM sleep). The sleep cycle repeats about four to five times every night. So you can see how a person has several different dreams in one night. Most people only remember dreams that happen closer to the morning when they are about to wake up. That you can't remember those dreams does not mean they never happened. The stages in the sleep cycle are organized by the changes in different brain activities.

Stage 1: You are entering into light sleep. In this stage, your eyes move rapidly. We call this NREM. The body gets relaxed and your body temperature lowers. Your heart rate lowers, too. The body is preparing to enter into deep sleep.
Stage 2: Also characterized by NREM. In this stage, the body temperature and heart rate drop again. You are completely asleep.
Stage 3: Still in the NREM stage, this is a deeper sleep still.
Stage 4: In this stage of sleep, your eyes move back or forward. We call it REM sleep. This stage happens at about 90-100 minutes after the beginning of sleep. Your blood pressure rises, heart rate speeds up. The majority of your dreams happen in this stage.
These stages repeat themselves throughout a night's sleep.

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    Imagine the situation. You are driving along a desert or on a mountain. You have no idea where you are. You passed the last house two hours ago. Then your car breaks down. It is night and it is cold. You have no mobile phone. What do you do? Well, next time take a GPS with you. This invention may be able to help you. It is a device(装置) which uses satellites (卫星) to find the user's position(位置). It can find your position to within 20 metres. A GPS cannot start your car, but at least you will know where you are.

    GPS, which means Global Positioning System, is a small radio receiver. It looks like a mobile phone. You can hold it in your hand, or put in your pocket. It is sometimes put into a watch or a telephone. We also find GPS devices in cars, planes, or boats. Some of these devices have electronic maps, so you know where you are. For example, in a city they can tell you the name of the street.

    There are three parts to the Global Positioning System. The first part is the receiver. You can hold it in your hand, or have it fixed into your car, plane, etc. The second part is a group of satellites orbiting the Earth. The receiver contacts at least four of the satellites and calculates(计算) its position. The third part of the system is a network of ground stations. They are all over the world. They control the satellites and make sure they are working well.

    Some people think that in the future the GPS will be as common as the mobile. They are becoming cheaper and more and more accurate(精确的). There are also new uses for the GPS. Perhaps they will become like watches. Everyone will have one and you will never be lost again.

    Robots come in many shapes and sizes. But most have one thing in common. They are built to help people, Lately engineers have been developing new kinds of robots. These high-tech machines are designed to lend a hand everywhere from hotels to disaster areas.

    "Robots help people by making their lives easier, safer, and more fun, "says engineer Omar.

    Since November, a robot named Pepper has been on the job at Mandarin Oriental Hotel in Las Vegas, Nevada. When guests have questions or need directions, they can ask Pepper. They can also use the robot's touch screen to find the information they need. Pepper is able to talk with guests and make them happy with stories too. It can even tell what kind of mood they are in.

    "Pepper provides our guests with information in an exciting and new way." says the hotel manager Donald Bowman.

    For a kid, being in the hospital can be boring and even scary. But a small robot called NAO is helping to make hospital stays easier. It was designed to keep people company.

    A Tennessee doctor named Phil Parker bought a NAO robot three years ago. He programmed(为…….编制程序)it to talk to and play with young patients. He brought it to hospitals to help sick kids. When kids get medical tests, NAO explains what is going on. The robot also reads to kids and plays games with them like Rock, Scissors ,Cloth(石头剪刀布).

    "The robot gets many kids to smile for the first time since they were in hospital," Parker says.

    Other robots are designed to help to save people in dangerous areas. For example, disaster areas can be full of broken stones and other dangers. Engineers in Japan are planning to build a robot called E2-DR to go into those areas and search for people who are hurt.

    Have you ever stayed in a hotel? Most Chinese hotels often provide guests with things like disposable (一次性的) toothbrushes, toothpaste, shampoo and slippers. Many guests like the idea because they don't have to bring their own. But, if you travel to Beijing, remember to bring your own things. Starting from June, some hotels in Beijing will no longer provide guests with these disposables. They want to ask people to use less disposable things.

    Many disposable things are made of plastic. People throw them away after only using them once. It is a waste of natural resources (资源) and is very bad for the environment. Do you know, one Chinese person makes as much as 400kg of waste a year! Most of that waste comes from disposable things. In Beijing, people throw away about 19,000 tons of plastic bags and 1,320 tons of plastic lunch bowls every year! Plastic can take between 100 and 400 years to break down. So the less plastic we throw out, the better. So, wherever you travel, bring your own things and use them again and again.

    Back at home and school, you can also do something to make our world a better place. Try to do these things in your daily life: Use cloth shopping bags, not plastic ones. After using a plastic bag, wash it out and let it dry. Then you can use it over and over again. Do not use paper cups. At your school canteen(食堂), use your own bowl and chopsticks instead of disposable ones.