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.

    Bioplastic(生物塑料) is a kind of plastic, but it is not the same as normal plastic. Normal plastic is made from chemical materials and takes a very long time to degrade(降解). But bioplastic is good for the environment. It is made by using bacteria(细菌) to process(加工) natural sources like vegetable oils, corn or sugar. It can degrade more easily.

    But there is a problem with bioplastic. The "food" that bacteria eat is what we eat. This means that bacteria are competing against humans for the same resources.

    Now scientists have found a new way to make bioplastic——using two kinds of bacteria and sunlight, according to Newsweek.

    One of the bacteria can use sunlight to produce sugar. The other kind lives in the salty waters of Bolivia. It eats the sugar that the first bacteria produce and then it can produce polymers(聚合物). Polymers are used to create bioplastics. The way the bacteria store polymers is similar as humans store fats.

    The new way to produce bioplastic has many advantages. It is 20 times faster than the normal way we produce bioplastic. Moreover, using these two bacteria saves resources.

    Firstly, producing a lot of bioplastic requires corn and sugar, which are used to feed normal bacteria. And growing corn and sugar needs farmland. But these two bacteria can just use sunlight. The land that is saved can be used to grow food for humans. Besides, this system doesn't need rich land or clean water at all, scientists said to Newsweek.

    The next problem scientists face is that they want to put their lab research into real-world practice. By doing this, bioplastic made with these two bacteria can be widely produced in the future.

    The monarch is one of the most beautiful butterflies. It is famous for its yearly migration（迁徙）from the northern part of North America to Mexico, There, millions of monarchs spend the winter together in one small area. This migration is one of the greatest wonders of nature. Yet this behavior has now put the monarch at risk.

    Every September, millions of monarchs from the United States fly to Mexico. After about two months of flying time, they reach their sanctuary(庇护所)in central Mexico. Then, in the warm climate of private and quiet valleys, far from most human activity, the butterflies create one of nature's great scenes. They cover every tree with bright color. The show lasts until spring, when the butterflies return north.

    While they are all crowded together, the monarchs are highly weak. If the environment in those valleys was disturbed, the whole species could be hurt or even die out. That is why for many years scientists who knew about the monarchs' winter sanctuary kept the location a secret.

    In recent years, however, the monarchs' secret has been discovered. Today, the butterflies' winter sanctuary is crowded with tourists, who disturb the environment. Worse still, local farmers who need more land to farm have begun to take up the area. They are cutting down trees, making it difficult for the butterflies to survive. They should not farm in the monarchs' sanctuary.

    People should act immediately to protect the species' winter sanctuary. Local farmers must be helped so that they no longer need to take land from the butterflies. Tourist visits to the butterflies' hidden valleys must also be limited. Unless these steps are taken soon, in a few years the monarch butterfly of North America may be just a beautiful memory.

    What is an egg? Birds and fish give birth to many babies at one time. They can do this by laying (产) many eggs. The baby birds or the baby fish stay in eggs until they are ready to be born. What do eggs look like? When you make a fried egg, you can see a yellow part and a white part. The yellow part of the egg becomes a chick. The chick eats the white part until it comes out of the egg.

    What is a fruit? Why do plants have fruits? A fruit is the house of seeds (种子). Plants grow flowers to make fruits. Fully grown fruits fall down. Then, the seed grow root (根) under the ground. What happens next? Another plant grows! Usually seeds grow inside of a fruit, but strawberry seeds grow outside of the fruit.

    Many scientists think that the Earth is getting warmer and warmer. If the change continues, the natural world and human society will face danger. Scientists believe human activity is responsible for the climate change. We produce too many greenhouse gases. They keep heat in the air and make the Earth warm.

    Many of the world's governments agree. And they want to solve the problem. So from 7 to 18 December, 2009，they held a conference in Copenhagen, Denmark to talk about global warming and climate change.

    Representatives(代表) from 192 countries and regions went to the meeting. Although they have not reached an agreement, the Copenhagen Accord(《哥本哈根协议》) was an important beginning to save the Earth. It was made by a small group of countries including China，the USA，India, Brazil and South Africa. Some other countries at the conference also showed support.

    What are the key points of the Copenhagen Accord? The accord limits global temperature increases to 2C by 2050. Scientists think it could help the world to avoid serious climate change.

    The accord also says that developed countries must promise to cut greenhouse gas emissions(排放) to the UN by 31 January, 2010. The accord asks developed countries to give money to help developing countries.

    Many countries and organizations are disappointed that the conference didn't reach a legal document(法律文书). And they think the accord is not clear enough about its goals.

African leaders are worried that the goal of a 2℃ global temperature increase isn't good enough, because it will mean a much higher increase in temperature across Africa. This could cause big problems like food and water shortages across the continent.

    Still, UN Secretary General believes the conference was an "improvement".

    "Finally we reached a deal," Ban said," the accord may not be everything everyone had hoped for, but this is an important beginning."