根据其内容简略回答问题。

    Canada Geese are large blue and white birds. When autumn comes, they have to fly south where the weather is warmer. The winters are so cold in Canada that the birds will die if they stay there.

    Last spring, Bill Lishman found sixteen young Canada Geese on his farm. They had lost their parents. Bill thought, “These young birds won't know what to do in the autumn.” He had a small plane and he decided to teach the birds to fly by following him. All through the summer, he went on short trips in his plane and the young geese flew after him.

    When the cold weather arrived in the autumn, Bill flew to Virginia in the United States--600 miles south of his home in Canada. The geese followed him all the way. Bill left the geese in Virginia and he returned home. This spring, Bill was waiting for the birds to come back. They didn't arrive, so Bill flew to Virginia to get them. He looked for them for two weeks but he couldn't find them. When he arrived back home, he found the geese waiting for him. They had found their way home without him!

    Alsten Chase has written a book about Yellowstone National Park. He is worried about the damage the fires can do to the park. He is also concerned(关心) about the park rules. These rules say that nature should decide what happens to the park. Alsten also writes that the elk herd(马鹿群) has grown too big. The elks walk on the riverbanks. They eat the new grass and roots of baby trees. The beavers(河狸) need the trees to build dams(坝).

    The dams raise the water levels. Higher water levels put more water into the soil. Wet soil helps plants grow faster. The plants offer homes and food to other animals.

    Chase thinks that the park rules would work only in a park with natural settings. He believes that Yellowstone has had an artificial(人为的) setting for a long time. The native people left. The wolves were taken away and other animals were removed. The areas of land were fenced off(隔开) and other animals added. He thinks the park rules that let herds grow too big and the fires are hurting the nature of the park.

    The park manager thinks the rules are good and that the park will be fine. Chase thinks the way the people run the park should be changed.

    As we know, all living things have to eat food. For a man, a tiger, a fish, a bird, or even a worm, food is needed. We know all living things are sure to die without food. In every part of the world, different kinds of animals share living places and live in communities (群落) together. They are connected(联系) in a food chain.

    In a food chain, some living things are producers and some are consumers. Plants are producers because they use sunlight, soil and other things to make their own food. Animals are consumers because they have to eat other animals or plants.

    There are four different kinds of consumers in the animal world. A carnivore is an animal that only eats other animals. An herbivore is an animal that only eats plants. An omnivore is an animal that eats plants and animals. A scavenger is an animal that eats dead animal.

    Here is a picture of a food chain. The food chain shows how animal eat each other in a community. In the picture, you can see what animal or plant is food for another animal. See? The grass is food for a rabbit(兔子), which then becomes food for a hungry tiger. In this way, all of these animals are connected.

    We always think that it's OK for us to leave our plants home during our vacation as plants won't scream like pets, right?

    A recent study done by a group of scientists at the Tel Aviv University has discovered that some plants will scream when they are under stress.

    The research was carried out on tomato plants and tobacco plants by cutting their stems (茎) and depriving (剥夺) them of water. A microphone was placed 10cm away from them. When their stems were cut, the plants started "screaming" between 20 and 100 kilohertz, and the scientists guess that this scream is probably meant to warn other plants nearby.

    When the tomato plants' stems were cut, 25 ultrasonic (超声的) pain sounds were recorded in an hour, and at the same time, 15 ultrasonic pain sounds were recorded from the tobacco plants. When they were deprived of water, the tomato plants recorded even more pain sounds with 35 pain sounds in an hour while the tobacco plants recorded about 11 pain sounds.

    The plants also acted differently to different kinds of stresses. For example, the tobacco plants gave out a stronger "scream" when they were deprived of water than when their stems were cut. But plants that were in no immediate (立刻的) danger gave out less than one ultrasonic sound per hour.

    The group of scientists said that plants are not as quiet as we had always thought, but in fact their voices are so high-pitched that we just can't hear them.

    Last year, another study has found out that plants feel pain when they are touched or hurt and they will give off a terrible smell.