A crow(乌鸦) is about twenty inches (英寸) long and black all over. Crows are dirty birds because they live on bad food. Crows eat a lot of waste food. In this way they are more useful to us than any birds. They clean up the dirty things in our streets. Crows are always hungry. They look for food all day, and in the evening you can see them in large numbers flying back to their nests(巢) in the trees. They sleep there at night.

    Crows are much noisier than other birds. Very often a large number of crows will get together on one house and talk. Sometimes they talk together, and sometimes they do it by turns(轮流) like human beings(人类). It is easy to tell(判断) from crow's sound if they are pleased or angry. Perhaps crows talk a lot because they are friendly birds. A pair of crows will live together all their lives, and if one of them dies, the other one becomes very sad and quiet for the rest of its life and some time later it dies too.

    It is a question that has confused parents for many years: why do children refuse to eat greens?

    Now, two American experts believe they have the answer.

    After studying dozens of babies as they played with various objects, the researchers noted that they were far more unwilling to touch plants than other things. They believe this is because evolution (生物进化) has biologically made children be wary of plants.

    Due to susceptibility (敏感性) to illness or injury in the early years of life, the body has designed an inner defence mechanism (内部保护机制) that limits a child' s contact with plants, they think. The researchers believe this is why children turn their noses up when faced with a plate of broad beans.

    The findings are published in a paper by Dr Annie E Wertz and Dr Karen Wynn, both psychologists at Yale University.

    They wrote, "Throughout human evolution... plants have been important in human's life. Yet, for all of these benefits, plants have always caused very real dangers."

    "Plants produce toxins (毒素) as defences that can be harmful, or even deadly. Some plants also produce physical defences, such as thorns（荆棘）can damage tissues (组织) and cause effects over the whole body."

    They added, "We predicted that babies may have behavioural strategies that reduce dangers caused by plants."

    To test their theory, the researchers studied how children aged eight to 18 months old reacted when presented with a variety of objects. It took much longer for children to grab plants; objects that were pretended to look like plants also caused a slow response time.

    For parents attempting to spoon some peas into the mouth of their child, this finding should come as welcome relief.

    In some science fiction movies, evil robots refuse to die, no matter how hard people fight back.

    Now science fiction has become science fact. For the first time, scientists have made a robot that can take a beating (挨打) and keep on going. Scientists from Cornell University made the robot, which looks like a spider with four legs.

    Until now, even the most advanced (先进的) robot was almost certain to break down when it was damaged. That is because its computer inside simply doesn't know how to make the machine work after its shape has changed.

    To deal with this problem, the scientists put eight motors (发动机) and two sensors (传感器) that read how the machine is working. They all give signals to the machine's software. Using this information, the computer can then figure out the machine's shape at any moment.

    The new technology is a big advance in robot-making, scientists say, and it's far from scary. It may someday help scientists create better artificial (假的) arms and legs and give new freedom to people who lose them. It might also help scientists understand how people and animals figure out their own sense of place in space.

    “It has been difficult to design robots that can work well when the environment changes or when it's damaged,” says Olaf Sporns of Indiana University in US. “With this work, we are nearer to solving this problem.”