Scientists are debating how to limit their newly-discovered power to change genetic structure (结构). Scientists already modify the genes (基因) of farm animals and agricultural plants to make them more productive or stronger. But now they can also change genes in wild animals and plants. These genes would continue into later generations. For example, it may be possible for scientists to remove from existence the kind of mosquitoes, small flying insects, that carry the Zika virus. They might also be able to permanently remove species (物种) of plants and animals that are damaging to other species.

    In a report published last week, the U. S. National Academies of Sciences, Engineering and Medicine (NAS) said it supports continued research on this kind of gene control. But it warned that it is not possible to know what will happen when these changed plants and animals are released (释放) into the wild.

    Sixteen biologists, ethicists (伦理学家) and policymakers are on an NAS committee that is examining the issue. They say that there is value to the new technology. But, they say, there is not enough evidence to support the release of modified organisms (生物体) from the laboratory into nature.

    Many people would support stopping mosquitoes and rats from carrying diseases. But scientists say we must understand the possible scientific, ethical, legal and social results of such action before we decide whether to take it. Gene modification is spread through reproduction (繁殖).

    Changed genes will continue to spread as long as an animal or plant continues to reproduce. They cannot be limited to a farm or kept within a country's borders. Scientists are wondering what may happen if a modified organism mates with another species. They are not yet sure how the modified genes would affect the other species. It is possible that those genes could harm those creatures or even lead to their disappearance from our planet.

    Along the river banks of the Amazon and the Orinoco there lives a bird that swims before it can fly, flies like a fat chicken, eats green leaves, has the stomach of a cow and has claws(爪)on its wings when young .They build their homes about 4.6m above the river ,an important feature(特征)for the safety of the young. It is called the hoatzin.

    In appearance, the birds of both sexes look very much alike with brown on the back and cream and red on the underside .The head is small, with a large set of feathers on the top, bright red eyes, and blue skin. Its nearest relatives are the common birds, cuckoos. Its most striking feature, though, is only found in the young.

    Baby hoatzins have a claw on the leading edge of each wing and another at the end of each wing tip .Using these four claws ,together with the beak(喙),they can climb about in the bushes, looking very much like primitive birds must have done. When the young hoatzins have learned to fly, they lose their claws.

    During the drier months between December and March hoatzins fly about the forest in groups of 20 to 30 birds, but in April, when the rainy season begins, they collect together in smaller living units of two to seven birds for producing purposes.

    Mark Twain left school when he was twelve. He had little school education. In spite of (尽管) this, he became the most famous writer of his time. He made millions of dollars by writing. His real name was Samuel Langhorne Clemens, but he is better known all over the world as Mark Twain, his pen-name.

    Mark Twain was born in 1835 and he was not a healthy baby. In fact, he was not expected to live through the first winter. But with his mother's tender care, he managed to survive. As a boy, he caused much trouble for his parents. He used to play jokes on all of his friends and neighbors. He didn't like to go to school, and he constantly ran away from home. He always went in the direction of the nearby Mississippi (密西西比河). He was nearly drowned (淹死) nine times.

    After his father's death in 1847, Mark twain began to work for a printer, who only provided him with food and clothing. Then, he worked as a printer, a river-boat pilot and later joined the army. But shortly after that he became a miner. During this period, he started to write short stories. Afterwards he became a full-time writer.

    In 1870, Mark Twain got married. In the years that followed he wrote many books including Tom Sawyer in 1876, and Huckleberry Finn in 1884, which made him famous, and brought him a great fortune (财富).

    Unfortunately, Mark Twain got into debts in bad investments (投资) and he had to write large numbers of stories to pay these debts. In 1904, his wife died, and then three of their children passed away.

    At the age of 70, his hair was completely white. He bought many white suits and neckties. He wore nothing but white from head to foot until his death on April 21, 1910.

Holidays

    My first impression of Miss Vicki was a highly authoritative(权威的) person towering over me. She spoke in a loud voice and the earth shook whenever she marched. That was in the first year of high school. She was a knowledgeable literature teacher then. However, during my first year in school, she struck terror into my heart(使我胆战心惊). And everyone else's of course. Just the mention of her name made the most unruly classes silent.

    Nevertheless, the two years of junior high passed by rather quickly. Soon, I went to senior high class. I had worked hard and gotten the subject combination that I wished for. Together with a group of old friends, I soon settled down in class comfortably.

    To everyone's surprise, she was fortunate enough to be my teacher that year. I was shocked when I heard the news. This time round, however, I decided not to hide in terror whenever she was near. I decided to face the fact that we were going to meet each other for the next 365 days. Instead of trying too hard to lick her boots, I tried my best to my natural self in front of her.

    Still, I could not shake off the ice-cold impression that she put in my heart. True, her jokes sometimes sent me into fits of laughter, yet at other times these jokes simply fell flat the moment she told them. My lovely class, however, was already ready to laugh at the right time of her amusing stories. After all, we would not want to run the risk of provoking(激怒) her.

    Unluckily, life was not to remain boring. One day we received news that Miss Vicki was to leave Singapore for the Philippines where she would take part in a voluntary teaching program for the poor. We did not know what to say actually. All of us cried at the airport.

    As any plane passenger will confirm, a crying baby is almost impossible to ignore, no matter how hard you try. Now scientists believe they may have worked out why. A baby's cry pulls at the heartstrings（扣人心弦）in a way while other cries don't, researchers found.

    Researchers found that a baby's cry can trigger unique emotional responses in the brain, making it impossible for us to ignore them—whether we are parents or not. Other types of cries, including calls of animals in great pain, fail to get the same response, suggesting the brain is programmed to respond specifically to a baby's cry.

A team of Oxford University scientists scanned the brains of 28 men and women as they listened to a variety of calls and cries. After 100 milliseconds — roughly the time it takes to blink (眨眼) —two parts of the brain that respond to emotion lit up. Their response to a baby's cry was particularly strong. The response was seen in both men and women—even if they had no children.

    Researcher Dr Christine Parsons said, “You might read that men should just notice a baby and step over it and not see it, but it's not true. There is a special processing in men and women, which makes sense from an evolutionary(演化的）view that both men and women would be responding to these cries.” The study was in people who were not parents, yet they are all responding at 100ms to these particular cries, so this might be a fundamental response present in all of us regardless of parental status.

    Fellow researcher Katie Young said it may take a bit longer for someone to recognize their own child's cries because they need to do more “fine-grained analysis”. The team had previously found that our reactions speed up when we hear a baby crying. Adults performed better on computer games when they heard the sound of a baby crying than after they heard recordings of adults crying.