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.

    While watching movies, it's getting hard to tell what is and isn't real. Thanks to computers, movie makers can now use their full imaginations. There's even a new type of character--made entirely by computers—which is getting more and more screen time.
    Making the impossible look easy has always been a part of movie magic. As far back as 1895, filmmakers used special effects in movies. Over the years, many few techniques（技术） were developed. Then, starting in the 1970s, computers took their place at the center of the process.
    One of the first movies to widely use 3D computer generated（生成的，产生的） imagery (CGI) was Tron(1982). In the following years, more CGI characters were brought to life, one by one. Then, Jurassic park (1993) brought us an island full of man-eating dinosaurs. Shortly afterwards, Toy Story (1995) became the first cartoon made entirely with 3D CGI effects. It was a big hit, and audiences loved the characters.
    By using “motion capture” technology, filmmakers can make the movements of CGI humans even more lifelike. With this technique, a real actor wears sensors（感受器，传感器） on his face and body. The sensors record the actor's movements and send the information to a computer. Then the movements are given to a CGI character. This technique was used to make the creature（生物，有生命的东西） Gollum in the second and third The Lord of the Rings movies (2002, 2003). Other films, like Beowulf (2007), have also used motion capture to help create CGI humans.
    It is still rather easy to tell that a CGI human is not real. But the technology is improving every year. Over time, many problems ( like the teeth and eyes looking fake) will be solved. We will certainly see more CGI animals, monsters, and people in movies and TV shows. The question is – in the future, how many real actors will be put out of work by computer actors?

      Astronauts are not like pilots, who fly into sky. They need some special trainings. They will fly into space. First they go to the Johnson space center in Houston Texas. They are tested there. Space doctors want to know how strong and smart they are.

      First of all, their hearts are tested. The people walk or run. Next, the space doctors see how fast their hearts are beating.

      Then it is another important test. In this test the person must curl his body up in a ball. And when he is in that position, he will be put into a round cloth bag. The doctors don't tell him how long he will have to stay in the bag. If a spaceship broke down in space, the astronauts would get into bags like these. Then they would have to wait, curled up in darkness, until they are saved. You can know that an astronaut must not be afraid of tight spaces or darkness.

      After these tests, scientists only choose the best people to start astronaut training in a training center. They will learn many other things in training. They will learn how to jump out of moving airplane, to blow up a lifeboat and get into it while they are in the ocean.

They also have to learn how to get lifted out of the ocean by a helicopter.

      When they finish training, the astronauts go on to work. They stay in good situation by running and doing exercise. They read about the special jobs. In that way they will be able to learn new facts about space travel.

      Finally, the astronaut is told to go to work on a flight into space. The members begin to know each other first. Then they can learn which jobs each will do.

D

    You don't need to get in a time-travelling machine to see how technology will change our lives, such as the way we shop. Several new technologies that are to change your buying habits already appear. Let's see what's in store for your future shopping.

    Try it on, virtually（虚拟地）. Want to shop online for a new pair of glasses? You don't need to guess which pair looks best on you—use the eBay Fashion iPhone app to try a pair of glasses you're checking out on a picture of your face. But what about buying something bigger? Thanks to Microsoft Kinect's action tracking（跟踪）camera, you can cover clothes on your screen body. You can even choose the background of your virtual fitting room to improve your shopping experience.

    Get a perfect, custom fit. Everyone's body is shaped differently. To get a perfect fit, you sometimes have to get your clothes changed. But by using 3D scanning technology, all the clothes you buy will fit your body perfectly. Some companies scan（扫描）your body using High-tech to get the real sizes, so they can make special clothes just for you.

    High-tech shopping carts（推车）and checkout counters（收银台）. High-tech shopping carts could be common in malls and supermarkets in the future. Microsoft Kinect-enabled carts are under test. The cart can follow you along the aisles（通道）, controlled only by your movement and your voice.

    In the United States, several supermarkets use a certain set called “Scan It” that gives buyers the freedom to scan products on their own while they shop. If we don't want to wait in line before the checkout counters, we can use Toshiba's new object Recognition Scanner. The machine identifies（辨认）a product as soon as it's placed in front of a camera just by its shape and color, even if it has no bar code.