In South America, the rich soil of the Amazon River basin in Brazil is known as "black gold". Scientists found that the secret of this rich soil was charcoal . Local people made it from animal bones and tree branches. They mixed the charcoal with the soil about 1.500 years ago. Now, scientists in the United States have done a modern demonstration. They say charcoal fertilization offers a revolutionary way to improve soil quality for hundreds or even thousands of years. Mingxin Guo and his team at Delavare State University heated tree leaves, corn stalks , small pieces of wood and poultry waste into "biochar" . They reported their findings at a recent meeting of the American Chemical Society in New Orleans. Biochar could be good news for farmers with poor soil and hungry populations to feed. Professor Guo says it could even help against global warming. Intensive  farming and overuse of chemical fertilizer give out carbon dioxide into the atmosphere. Biochar does the opposite, he says. It traps carbon in the ground. The researchers planted winter wheat in containers of soil in a greenhouse -- some with biochar, some without. Professor Guo says the wheat grows much better in the pots with biochar. The soil was added two percent charcoal to. But he says even a one percent treatment will increase productivity. The results demonstrated that biochar can increase organic matter in soil. Loss of nutrients in soil is an increasing problem worldwide as farmers try to grow more food for growing populations. Next, the team will carry out a five-year study of biochar with spinach , green peppers and tomatoes. Mingxin Guo says he learns about the "black gold" in Brazil from a magazine story. He explains that it was discovered in the jungle, in the area where waters flow to the Amazon, in the 1960's. But it was not until recent years that scientists began to bring public attention to it. Biochar has the following advantages EXCEPT that   _  . A) it can improve the condition of the soil B) it can be used as a kind of energy C) it can help against global warming D) it can increase productivity of the corn
B


(Question)
These days, it's easy to fly across oceans for vacation. Centuries ago, however, crossing the open seas required thorough and accurate planning, handmade boats, and courage. Scientists and historians have long been looking for clues to explain who crossed which oceans first. When it comes to the trip between Polynesia   and South America, chickens may have been among the first ocean voyagers, according to new evidence.     After studying an ancient chicken bone, anthropologists   from the University of Auckland in New Zealand now say that people and chickens traveled from Polynesia to what is now Chile   by about 620 years ago. By then, the Inca people were already living in South America, but the Polynesians would have been the first to get there by sea. Previous theories claimed that European explorers and their chickens sailed to South America first -- but those voyagers didn't arrive until about a century later.    In 2002, archaeologists dug up 50 chicken bones from a site in Chile called El Arenal. The team from New Zealand analyzed one to these bones. According to their calculations, the bone is about 650 years old.    The researchers also compared the genetic material, or DNA, from the South American chicken bone with DNA from 11 chicken bones that had been found on the Polynesian islands of Tonga and American Samoa. These islands are 6,000 miles west of Chile. The bones found on the Polynesian islands are been 600 and 2,000 years old.    Results of the comparisons showed that the chicken bones from both the Polynesian and South American sites had part of DNA in common. The researchers found the same part of DNA in feathers of two living chickens in Chile that belong to a modem breed that lays blue eggs. That DNA evidence suggests a close relationship among the chickens.    "However, the weight of scientific evidence is now behind the hypothesis   that it was seafaring ( ) Polynesians who sailed from the islands to South America and returned," says archaeologist Patrick V. Kirch of the University of... What do we learn from the passage? A) European explorers and their chickens were the first to sail to South America. B) Chickens in South America have the same ancestors as those in Polynesia. C) In ancient times, a 6,000-mile channel separated Polynesia from South America. D) Before the Polynesians arrived in South America, the Inca people had lived there.
(Answer)
D


Question: prefix = st1 /Gland, Switzerland - Rivers on every continent are drying out, threatening severe water shortages, according to a new WWF report. The report, World's Top Rivers at Risk, released ahead of World Water Day (22 March), lists the top ten rivers that are fast dying as a result of climate change, pollution and dams. "All the rivers in the report symbolize the current freshwater crisis, which we have been signalling for years," says WWF Global Freshwater Programme Director Jamie Pittock. "Poor planning and inadequate protection of natural areas mean we can no longer assume that water will flow forever. Like the climate change crisis, which now has the attention of business and government, we want leaders to take notice of the emergency facing freshwater now not later."  Five of the ten rivers listed in the report are in Asia alone. They are the Yangtze, Mekong, Salween, Ganges and Indus. Europe's Danube, the America'sLa Plataand Rio Grande/Rio Bravo, Africa's Nile-Lake Victoria andAustralia's Murray-Darling also make the list. Dams along the Danube River -- one of the longest flowing rivers in Europe -- have already destroyed 80 per cent of the river basin's wetlands and floodplains. Even without warmer temperatures threatening to melt Himalayan glaciers, the IndusRiverfaces scarcity due to over-extraction for agriculture. Fish populations, the main source of protein and overall life support systems for hundreds of thousands of communities worldwide, are also being threatened. The report calls on governments to better protect river flows and water allocations in order to safeguard habitats and people's livelihoods. "Conservation of rivers and wetlands must be seen as part and parcel of national security, health and economic success," Pittock adds. "Emphasis must be given to exploring ways of using water for crops and products that do not use more water than necessary." In addition, cooperative agreements for managing shared resources, such as the UN Watercourses Convention, must be ratified and given... According to the passage, which of the following is not the cause of severe water shortage? A) Globe warming B) Less rainfall C) Pollution D) Poor planning
Answer:
B