A

      There are too many cities around the world. And each city needs water in many ways. Water on Earth falls mainly as rain. So the rainfall (降雨量) is important to each part of the world. And it is different from one city to another. The following chart shows the average (平均的) rain fall in four different cities in July and January.

C

    Different weather makes people feel different.It has an effect on health，intelligence(智力) and feelings.

    In August，it is very hot and wet in the southern part of the United States.People there have heart trouble and other kinds of health problems during this month.In the Northeast and the Middle West，it is very hot at some times and very cold at other times.People in these states have more heart trouble after the weather changes in February or March.

    The weather can also influence intelligence.For example，in a 1983 report by scientists, the IQ(智商) of a group of students was very high when a very strong wind came，but after the strong wind，their IQ was 10% lower.The wind can help people have higher intelligence.Very hot weather，on the other hand，can make it lower.Students in many schools of the United States often get worse in exams in the hot months of the year(July and August)．

    Weather also has a strong influence (影响)on people's feelings.Winter may be a bad time for thin people.They usually feel cold during these months.They might feel unhappy during cold weather.But fat people may have a hard time in hot summer.At about 18℃，people feel more comfortable.

    Are you feeling sad，tired，or unhappy today？It may be the weather's problem.

    Many people have dogs at home as pets. If a dog is happy, then he may want to meet you or play with you. If he doesn't feel happy, then he would rather stay alone. But dogs can't talk. How can you tell how your dog is feeling? By his body language.

    If your dog's head and back are lowered, his ears are down and his eyes are narrowed, and his tail is between his legs, then he is fearful. You may touch him gently to comfort him. If your dog's ears are up, his eyes are bright, and he wags his tail rapidly (快速地), he is very happy. He may also hold his mouth open more or even pant (气喘) mildly. Then you can go and play with him freely. If he closes his mouth and looks serious as you get closer, then he has changed his mind. It is better to leave him alone until he comes to you. Remember, we are talking about dogs that you know. Be sure a parent is around to allow you to get close to the dog. Get away from strange dogs even if they seem friendly.

    The most important clue (线索) is the mouth. If the dog's mouth is closed, then he is most likely to be not relaxed or happy, and he does not want you to touch or play with him right now.

    The best time to collect green leaves is early in summer but not so early. The months of June and July provide the best leaf samples (样本) but you can find great leaf samples throughout the summer. To make a full colour collection, you have to collect leaves in autumn. I have seen many beautiful fall colour collections.

    When you select leaves for your collections, try to select leaves of about the same size and shape on the tree. Make sure you should collect the complete leaves.

    Remember, simple leaves have only one blade (叶片) or leaflet. Compound leaves have several or many leaflets. You must know these two kinds of leaves. Good leaf collections contain the entire leaf. That is a small part of the twig (嫩枝) with a lateral or terminal bud (芽).

    When you collect leaves in the field, you can place them between the pages of a magazine to protect them. And then, press them as soon as possible before you remove them from this magazine. You should dry the collected leaves carefully before placing them in a leaf press. Finally, place them in a leaf press. You should write down each leaf's name and these names should follow the leaves until the exhibition comes.

    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."