阅读下列短文，从每题所给的A、B、C、D四个选项中选出最佳答案。

    All living things need energy to live and grow. This energy comes first from the sun. Plants use water and sunlight to make their own food. Animals can not make their own food, and they eat plants. Other animals then eat the plant eaters.

    A food chain shows what eats what. It might show that zebras eat grass and then lions eat zebras.   

    Lions also eat other animals. Zebras eat other kinds of plants. So it takes more than one food chain to show how lions and zebras get their energy.

    A food web shows how food chains work together. From it we can see how energy moves from plants to animals.

    Plants and animals that live in hot, dry deserts depend on water as well as food. Creosote bushes have small leaves that hold water. Their seeds provide food and water for kangaroo rats. Kangaroo rats don't need to drink water. They get all the water they need from the plants they eat. Kangaroo rats keep cool by coming out only at night to look for food. Ringtail cats also come out only at night. Ringtail cats hunt and eat kangaroo rats. Coyotes eat both the kangaroo rats and the ringtail cats.

    Nothing is wasted in a food wed. Vultures eat dead animals. Vultures are scavengers. Scavengers do not hunt and kill other animals to get food. They eat animals that are already dead. When a ringtail cat or a coyote dies, it makes a meal for the vultures. Scavengers do an important job in keeping the environment clean.

    Some primary schoolchildren have been raised in homes with more green space around. They are likely to come with larger volumes of white and grey matter in certain areas of the brain. These differences are associated(关联) with beneficial effects on cognitive function (认知功能). This is the main conclusion of a study led by the Barcelona Institute for Global Health.

    The study was performed among 253 schoolchildren in Spain .Lifelong exposure(接触) to green space in the living places was recorded—using the information on the children's addresses from birth up through to the time of the study. Brain structure was studied using 3D magnetic resonance imaging (MRI). Working memory and inattentiveness(注意力不集中)were graded with computers.

    “This is the first study that shows the association between long-term exposure to green space and brain structure.” Says Dr. Payam Dadvand, the leading researcher of the study, “Our findings suggest that exposure to green space early in life could result in beneficial structural changes in the brain.”

    The findings show that long-term exposure to greenness is positively associated with white and grey matter volumes in several parts of the brain. Some of them are related to higher scores on cognitive tests. Moreover, larger volumes of white and grey matter in those parts might lead to better working memory and less inattentiveness.

    Exposure to nature has been thought to be necessary for brain development in children. Another study of 2,593 children shows that children in school with more green space have a greater increase in working memory and a greater decrease in inattentiveness.

    Humans are believed to be tied to nature.  Playing in greener areas offers children opportunities to search and learn. Accordingly, green space is thought to prompt important exercises in discovery, creativity and risk taking. These exercises in turn positively influence brain development.

    Dr. Dadvand's study suggests how such structural changes could bring about the beneficial effects of green spaces on cognitive development, it also adds to the proof that suggests the lasting effects of early life exposure to greenness on our health and the benefits of increasing greenness in cities.

    Further studies are needed to prove the findings in other populations, settings and climates. And researchers need to examine differences according to the nature and quality of green space.

    Mint (薄荷) is a useful plant. You can see it in different kinds of dishes. Mint can bring us many health advantages. It can also help us relax. Don't you believe it? Just smell the plant when you feel tired.

    Now, if you love mint, you don't have to buy it at the market. The plant is very easy to grow. You can plant it all year round, and it can grow well both indoors and outdoors.

    ①Prepare your flower pot (盆)

    Fill your flower pot with soil. Fill soil to a depth (深度) of about 25 centimeters. Use a garden fork to loosen the soil (松土).

    ②Plant your mint

    Plant your mint seeds (种子) 40 centimeters far from each other. If your pot is small, use just one plant or seed.

    ③Put your plant in a proper place

    Mint loves sunlight, but it also likes a bit of shade. Put your plant in a place where it can get both sunlight and shade.

    ④Water your mint

    Mint prefers wet soil. Keep the soil well watered, but don't overdo it. Don't forget to put a plant plate under your pot.

    ⑤Time to harvest

    Mint grows fast. After your plant grows up, you can pick its leaves at any time.

    To make things more fun, why not ask each of your classmates to grow some mint? Let's see whose mint grows the fastest!

    The world's first hydrogen-powered(氢动力) trains have begun running in Germany last month. The new trains will run 100-kilometer trips and can travel up to 140 kilometers an hour.

    A French railroad company called Alstom built two hydrogen-powered trains. Teams in Germany and France cooperated on the project, which was supported by the German government. The new train model, called the Coradia iLint, signals the beginning of efforts in Germany and other nations to move away from pollution-producing diesel(柴油) trains.

    Compared(与…相比较) with diesel trains, the Coradia iLint is designed to run on non-electrified train lines with low levels of noise. It uses a process that combines hydrogen and oxygen to produce electrical power. If the system produces more energy than the train needs at that time, it can store the extra energy in batteries. The only emissions(排放物)are water and steam.

    A single tank of hydrogen can run a Coradia iLint train for about 1,000 kilometers. This is very similar to the distance a diesel-powered train can run on with a single tank.

    Hydrogen-powered trains cost more than diesel trains to build. But Alstom officials say the operating costs are much lower. The company plans to provide another 14 Coradia iLint trains by the year 2021. Several other European countries have also expressed interest in developing hydrogen train systems. France has already said it wants its first hydrogen train to be operated by 2022.