阅读下面四篇短文，从每题所给的A、B、C、D四个选项中选出最佳选项。

C

    Indian scientists have designed a new device that they hope will solve one of the biggest problems with the use of solar energy. They call the device a solar tree. Solar trees have metal “branches” which are just from a tall pole at different levels. Each branch holds a solar panel*. These panels have large metal boards that collect energy from the sun and turn it into electricity.

    Daljit Singh Bedi is the main scientist at the Council of Scientific and Industrial Research in India. Bedi says the shape of the solar trees makes it possible to fit more solar panels in a space than traditional systems do. This means less land would be needed to produce solar energy. “It takes about four square meters of space to produce energy which may need 400 square meters of space,” he says.

     Scientists believe the energy a solar tree collects will be enough to power five homes. The solar tree will make it easier to provide solar energy for homes in cities. The trees will also take less space from farmers in rural areas. Bedi says solar trees will collect more energy than normal solar panels on the tops of buildings. “This design makes the solar panels exposed more towards the sun,” he says. “And that way people are able to use 10 to 15 percent more energy.”

    India has promised to reduce its greenhouse gas production. The country's promise depends heavily on increasing solar energy. The cost of solar panels has gone down in recent years. This has increased the possibility of applying solar trees in India.

    Amit Kumar is the senior director of the Energy and Resources Institute in New Delhi. He says gaining access to land takes time and increases costs. He adds that it is still not clear how useful these new developments in solar power technology are. “Only when we put those trees on a large scale will we be able to get that answer,” he says.

    Energy is everywhere. We use energy every day.

    Electricity is a form of energy and this is what powers the TV, hairdryer, phone, fridge, electric toothbrush and more! Our growing need for energy is one of the problems facing the world today, because producing electricity also produces pollution.

    Here are some simple ways to make a big difference when using electricity.

On or off? Leaving televisions and computers on with the little red light showing still uses electricity, even though they might look like they're turned off. To stop this you can turn them off.

    Lights out! Turning lights off when you're not in the room can save a lot of energy.

    Fridge door closed. The fridge is an important part of the kitchen, because it keeps food fresh, cool and healthy! But it takes a lot of energy to keep cool, so try not to leave the fridge door open or put hot things inside.

    Use the sun's energy. An increasing number of people are fitting solar panels（太阳能电池板） to their houses. They create electricity from sun-light, which can then be used to power our homes. Solar heating panels make hot water, reducing the need for electricity or gas.

    The expression "lanshouxianggu" has been quite popular on Chinese social networking sites. You may have used it many times when chatting online. However, did you know that the "blue thin mushroom" was not just magic of Photoshop and was really there in nature?

    Well, let' s meet Entoloma hochstetteri (霍氏粉褶菌).This is a kind of naturally-blue fungus(真菌) The plant looks very small. Its sten' s diameter(梗的直径) measures only about 5 millimeters. Entoloma hochstetteri can be found widely in New Zealand, especially on the west coast. The Maori name for it is "werewere-kokako." It seems New zealand is very proud of producing this unusual species-the country prints the blue mushroom on its $50 notes.

    Athough the species is very unusual, little is known about it. Silas villas-boas is a scientist at the University of Auckland. He said he was very disappointed that nobody had ever tried to test the blue mushroom in the lab, "You can even count the number of scientific articles on it on one hand, he said. The scientist decided to be the first to study the plant. A group of researchers have been helping him with the study.

    In an early test, the researchers found alkaloids(生物碱) and Omega-3 fatty acids(w-3脂肪酸)in the blue mushroom. While the acids are helpful to health, alkaloids soetimes influence how the brain works. However, Villas-Boas said the substance was very common in plants. So far, the researchers have not found any toxins(毒素) in Entoloma hochstetteri, but they are not yet sure if it can be eaten. Villas-Boas said more testing would be required.

    Animals can move from place to place, but plants cannot. When an animal is under attack, it can run away or fight back. Plants certainly cannot run away, and they have no teeth or claws. But plants can protect themselves in both physical and chemical ways.

    Some plants have their own ways to keep animals away. For example, the leaves of the holly(冬青) have sharp prickles(刺) that discourage grass-eating animals. Holly leaves on lower places have more prickles than leaves on upper places. This is because the lower leaves are easier for most animals to reach. Some plants, such as the oak trees(橡树), have thick and hard leaves that are difficult for animals to eat. Some grasses may contain a sandy material, and eating such grasses wears down the animals' teeth. Many plants also have chemical defenses. Some plants produce chemicals that taste bitter(苦) or cause an unpleasant reaction. Some plants may fight against an attack by increasing the production of these chemicals. When a worm bites a tobacco leaf (烟叶), the leaf produces a chemical smell. Many plants depend on both physical and chemical defenses. A certain plant in China, for instance, has prickly leaves, and each prickle has poisonous water(毒液). Only one experience with this kind of plant will teach an animal to stay away from it in the future.

    Have you ever paid attention to the Air Quality Index (空气质量指标) or AQI reported in the newspaper? The AQI helps us understand what the air quality around us means to our health. The AQI uses colors, numbers and words to tell us about the air. Let's see what these colors and numbers mean.