Experiments under way in several labs aim to create beneficial types of genetically modified foods, including starchier potatoes and caffeine-free coffee beans. Genetic engineers are even trying to transfer genes from a cold-winter fish to make a frost-resistant tomato.

    A low-sugar GM strawberry now in the works might one day allow people with health problems such as diabetes (糖尿病) to enjoy the little delicious red fruits again. GM beans and grains rich in protein(蛋白质) might help people at risk of developing kwashiorkor. Kwashiorkor, a disease caused by severe lack of protein, is common in parts of the world where there are severe food shortages.

    Commenting on GM foods, Jonathon Jones, a British researcher, said: "The future benefits will be enormous（巨大的）, and the best is yet to come". To some people, GM foods are no different from unmodified foods. "A tomato is a tomato," said Brian Sansoni, an American food manufacturer.

    Critics of GM foods challenge Sansoni's opinion. They worry about the harm that GM crops might do to people, other animals, and plants.

    In a recent lab study conducted at Cornell University, scientists tested pollen(花粉) made by BT corn, which makes up one-fourth of the U.S. corn crop. The scientist dropped the pollen onto milkweed, a plant that is the only known food source of a butterfly caterpillar(毛虫). Within four days of feeding on the leaves, almost half of a test group of caterpillars died. "This is a warning bell." said Cornell researcher Linda Raynor.

    Some insects that are not killed by GM foods might find themselves made stronger. How so? The insecticides are used on the crops to kill the pests. But GM plants produce a continuous level of insecticide. Insects relying on those crops may develop resistance to the plants and they may also develop a resistance to the insecticide.

    At the forum on GM food held last year in Canada. GM crops that have been made resistant to the herbicide might crossbreed with wild plants, creating "superweeds" that could take over whole fields.

    So where do you stand? Should GM food be banned in the United States, as they are in parts of Europe? Or do their benefits outweigh（胜过） any of the risks they might carry?

    One day when I was 12, my mother gave me an order: I was to walk to the public library, and borrow at least one book for the summer. This was one more weapon for her to defeat my strange problem—inability to read.

    In the library, I found my way into the “Children's Room.” I sat down on the floor and pulled a few books off the shelf at random. The cover of a book caught my eye. It presented a picture of a beagle. I had recently had a beagle, the first and only animal companion I ever had as a child. He was my secret sharer, but one morning, he was gone, given away to someone who had the space and the money to care for him. I never forgot my beagle.

    There on the book's cover was a beagle which looked identical (相同的) to my dog. I ran my fingers over the picture of the dog on the cover. My eyes ran across the title, Amos, the Beagle with a Plan. Unknowingly, I had read the title. Without opening the book, I borrowed it from the library for the summer.

    Under the shade of a bush, I started to read about Amos. I read very, very slowly with difficulty. Though pages were turned slowly, I got the main idea of the story about a dog who, like mine, had been separated from his family and who finally found his way back home. The dog was my dog, and I was the little boy in the book. At the end of the story, my mind continued the final scene of reunion, on and on, until my own lost dog and I were, in my mind, running together.

    My mother's call returned me to the real world. I suddenly realized something: I had read a book, and I had loved reading that book. Everyone knew I could not read. But I had read it. Books could be incredibly wonderful and I was going to read them.

    I never told my mother about my “miraculous” (奇迹般的) experience that summer, but she saw a slow but remarkable improvement in my classroom performance during the next year. And years later, she was proud that her son had read thousands of books, was awarded a PhD in literature, and authored his own books, articles, poetry and fiction. The power of the words was held.

    Mr. Jackson was tired of living in his old house in the countryside and wanted to sell it and buy a better one. He tried to sell it for a long time, but was not successful, so at last he decided to go to an estate agent（房产经纪人）.

    The agent advertised the house straight away, and a few days later, the owner saw a very beautiful photograph of his house, with a wonderful description of his garden in an expensive magazine.

    Having read the advertisement through, the house owner hurried to phone the estate agent, saying, “I'm sorry, Mr. Jones, but I've decided not to sell my house after all.” “Why?” the agent asked in a surprised voice. “Because from the advertisement in that magazine I can see it's just the kind of house I've wanted to live in all my life.”

    We know that many animals do not stay in one place. Birds, fish and other animals move from one place to another at a certain time. They move for different reasons: most of them move to find food more easily, but others move to get away from places that are too crowded.

    When cold weather comes, many birds move to warmer places to find food. Some fishes give birth in warm water and move to cold water to feed. The most famous migration(迁移) is probably the migration of the fish, which is called “salmon”. This fish is born in fresh water but it travels many miles to salt water. There it spends its life. When it is old, it returns to its birthplace in fresh water. Then it gives birth and dies there. In northern Europe, there is a kind of mouse. They leave their mountain homes when they become too crowded. They move down to the low land. Sometimes they move all the way to the seaside, and many of them are killed when they fall into the sea.

    Recently, scientists have studied the migration of a kind of lobster(龙虾). Every year, when the season of bad weather arrives, the lobster get into a long line and start to walk across the floor of the ocean. Nobody knows why they do this, and nobody knows where they go.

    So, sometimes we know why humans and animals move from one place to another, but at other times we don't. Maybe living things just like travel.

    For thousands of years, people have known that the best way to understand a concept is to explain it to someone else. "While we teach, we learn," said Roman philosopher Seneca. Now scientists are bringing this ancient wisdom up to date. They're documenting why teaching is such a fruitful w ay to learn, and designing creative ways for young people to take part in instruction.

    Researchers have found that students who sign up to tutor others work harder to understand the material, recall it more accurately and apply it more effectively. Student teachers score higher on tests than pupils who're learning only for their own sake. But how can children, still learning themselves, teach others? One answer: They can tutor younger kids. Some studies have found that first-born children are more intelligent than their later-born siblings(兄弟姐妹). This suggests their higher IQs result from the time they spend teaching their siblings. Now educators are experimenting with ways to apply this model to academic subjects. They arrange college undergraduates to teach computer science to high school students, who in turn instruct middle school students on the topic.

    But the most cutting-edge tool under development is the "teachable agent" — a computerized character who learns, tries, makes mistakes and asks questions just like a real-world pupil.

    Computer scientists have created an animated(动画的)figure called Betty's Brain, who has been "taught" about environmental science by hundreds of middle school students. Student teachers are inspired to help Betty master certain materials. While preparing to teach, they organize their know ledge and improve their own understanding. And as they explain the information to it, they identify problems in their own thinking.

    Feedback from the teachable agents further improves the tutors' learning. The agents' questions forces student tutors to think and explain the materials in different ways, and watching the agent solve problems allow s them to see their know ledge put into action.

    Above all, it's the emotions one experiences in teaching that improve learning. Student tutors feel upset when their teachable agents fail, but happy when these virtual pupils succeed as they develop pride and satisfaction from someone else's accomplishment.