单选题Why is it difficult to detect neutrinos?

单选题Most plants can make their own food from sunlight, (1) some have discovered that stealing is an easier way to live, Thousands of plant species get by (2) photosynthesizing, and over 400 of these species seem to live by pilfering sugars from an underground (3) of fungi(真菌). But in (4) a handful of these plants has this modus operandi been traced to a relatively obscure fungus. To find out how (5) are (6) , mycologist Martin Bidartondo of the University of California at Berkeley and his team looked in their roots. What they found were (7) of a common type of fungus, so (8) that it is found in nearly 70 percent of all plants. The presence of this common fungus in these plants not only (9) at how they survive, says Bidartondo, but also suggests that many ordinary plants might prosper from a little looting, too. Plants have (10) relations to get what they need to survive. Normal, (11) plants can make their own carbohydrates through photosynthesis, but they still need minerals. Most plants have (12) a symbiotic relationship with a (13) network of what are called mycorrhizal fungi, which lies beneath the forest (14) . The fungi help green plants absorb minerals through their roots, and (15) , the plants normally (16) the fungi with sugars, or carbon. With a number of plants sharing the same fungal web, it was perhaps (17) that a few cheaters—dubbed epiparasites—would evolve to beat the system. (18) , these plants reversed the flow of carbon, (19) it into their roots from the fungi (20) releasing it as "payment./

单选题 In some ways, the United States has made spectacular progress. Fires no longer destroy 18,000 buildings as they did in the Great Chicago Fire of 1871, or kill half a town of 2,400 people, as they did the same night in Peshtigo, Wisconsin. Other than the Beverly Hill Supper Club fire in Kentucky in 1977, it has been four decades since more than 100 Americans died in a fire. But even with such successes, the United States still has one of the worst fire death rates in the world. Safety experts say the problem is neither money nor technology, but the indifference of a country that just will not take fires seriously enough. American fire departments are some of the world's fastest and best-equipped. They have to be. The United States has twice Japan's population, and 40 times as many fires. It spends far less on preventing fires than on fighting them. And American fire-safety lessons are aimed almost entirely at children, who die in disproportionately large numbers in fires but who, contrary to popular myth, start very few of them. Experts say the fatal error is an attitude that fires are not really anyone's fault. That is not so in other countries, where both public education and the law treat fires as either a personal failing or a crime. Japan has many wood houses; of the estimated 48 fires in world history, that burned more than 10,000 buildings, Japan has had 27. Penalties for causing a severe fire by negligence can be as high as life imprisonment. In the United States, most education dollars are spent in elementary schools. But the lessons are aimed at a too limited audience; just 9 percent of all fire deaths are caused by children playing with matches. The United States continues to rely more on technology than laws or social pressure. There are smoke detectors in 85 percent of all homes. Some local building codes now require home sprinklers. New heaters and irons shut themselves off if they are tipped.

单选题John Doerr called the boom in the 1990s the "largest single legal creation of wealth" because

单选题When Marine Lt. Alan Zarracina finally did the splits after months of struggling with the difficult pose in yoga class, the limber women around him applauded. Zarracina, a 24-year-old Naval Academy graduate and flight student, admits he would have a hard time explaining the scene to other Marines. Each class ends with a chant for peace. Then, instructor Nancy La Nasa hands students incense sticks as a gift for their 90 minutes of back bends, shoulder stands and other challenging positions. Zarracina has tried to drag some of his military friends to class, but they make fun of hint. "It's not necessarily considered masculine,' he said. Still, the popular classes, based on ancient Hindu practices of meditation through controlled breathing, balancing and stretching, are catching on in military circles as a way to improve flexibility, balance and concentration. A former Navy SEAL told Zarracina about the class. The August edition of Fit Yoga, the nation's second-largest yoga magazine with a circulation of 100,000, features a photo of two Naval aviators doing yoga poses in full combat gear aboard an aircraft carrier. "At first it seemed a little shocking--soldiers practicing such a peaceful art," writes editor Rita Trieger. Upon closer inspection, she said, she noticed "a sense of inner calm' on the aviators' faces. "War is hell, and if yoga can help them find a little solace, that's good,' said Trieger, a longtime New York yoga instructor. Retired Adm. Tom Steffens, who spent34 years as a Navy SEAL and served as the director of the elite corps' training, regularly practices yoga at his home in Norfolk, Va. "Once in a while I'll sit in class, and everyone is a 20-something young lady with a 10-inch waist and here I am this old guy, ' he joked. Steffens, who said the stretching helped him eliminate the stiffness of a biceps injury after surgery, said the benefits of regular practice can be enormous. "The yoga cured all kinds of back pains," he said. "Being a SEAL, you beat up your body." Yoga breathing exercises can help SEALs with their diving, and learning to control the body by remaining in unusual positions can help members stay in confined spaces for long periods, he said. "The ability to stay focused on something, whether on breathing or on the yoga practice, and not be drawn off course, that has a lot of connection to the military," he said. "In our SEAL basic training, there are many things that are yoga-like in nature.

单选题 Until about four decades ago, crop yields in agricultural systems depended on{{U}} (1) {{/U}}resources, recycling organic matter, built-in biological control mechanisms and rainfall patterns. Agricultural yields were{{U}} (2) {{/U}}but stable. Production was{{U}} (3) {{/U}}by growing more than one crop or variety in space and time in a field as insurance against pest{{U}} (4) {{/U}}or severe weather. Inputs of nitrogen were{{U}} (5) {{/U}}by rotating major field crops with legumes. In turn, rotations suppressed insects, weeds and diseases by effectively{{U}} (6) {{/U}}the life cycles of these pests. A typical corn belt farmer grew corn{{U}} (7) {{/U}}with several crops including soybeans, and small grain production was intrinsic to maintain livestock. Most of the labor was done by the family with occasional hired help and no{{U}} (8) {{/U}}equipment or services were purchased from off4arm sources. In these type of farming systems the link between agriculture and ecology was quite{{U}} (9) {{/U}}and signs of environment degradation were seldom evident. But as agriculture modernization{{U}} (10) {{/U}}the ecology-farming linkage was often broken as ecological principles were{{U}} (11) {{/U}}. In fact, several agricultural scientists have arrived at a{{U}} (12) {{/U}}consensus that modem agriculture confronts an environment crisis. A growing number of people have become concerned about the long-term{{U}} (13) {{/U}}of existing food production systems. Evidence has shown that{{U}} (14) {{/U}}the present capital-and-technology-intensive fanning systems have been extremely productive and competitive, they also bring a{{U}} (15) {{/U}}of economic, environmental and social problems. Evidence also shows that the very nature of the agricultural structure and prevailing polices have led to this environmental{{U}} (16) {{/U}}by favoring large farm size, specialized production, crop monocultures and mechanization. Today as more and more farmers are integrated{{U}} (17) {{/U}}international economies, imperatives to{{U}} (18) {{/U}}disappear and monocultures are rewarded by economies of scale. In turn, lack of rotations and diversification{{U}} (19) {{/U}}key self-regulating mechanisms, turning monocultures into highly{{U}} (20) {{/U}}agro-ecosystems dependent on high chemical inputs.

单选题The author's tone is ______.

单选题We learn from the passage that an emotion is created by something ______.

单选题Which of the following would be the best title?______

单选题Whether a job can be classified as labor or work depends on______.

单选题According to the passage, when was the new planet first detected?

单选题Kevin Hines, a manic-depressive, was 19 and in one of his weekly downswings on an overcast Monday morning in 2000. He went to the nearby Golden Gate Bridge to kill himself mostly because, with only a four-foot (1.2-metre) railing to leap, "I figured it was the easiest way." He dived over, but flipped and hit the water at 75mph with his feet first. His legs were crushed, but he somehow stayed conscious and started paddling with his upper body until the Coast Guard fished him out. Mr. Hines is one of 26 people who have survived suicide attempts at the bridge, but 1 223 are known to have succeeded (i. e., were seen jumping or found floating). People are throwing themselves off the bridge at the rate of two a month, which makes it the most popular place in the world for suicides. One book on the subject says that the Golden Gate is "to suicide what Niagara Falls is to honeymooners". Many San Franciscans think that the solution is to emulate the Empire State Building, the Sydney Harbour Bridge, the Eiffel Tower, St. Peter's basilica and other such places and put up a simple barrier. This, however, is a decision for the 19 board members of the Golden Gate Bridge, Highway and Transportation District, an entity that oversees the bridge itself and the buses and ferries that operate in the area. Most of its revenues' come from tolls and fares, and the district loses money. A barrier would cost between $15 million and $ 25 million. So the Psychiatric Foundation of Northern California, which has adopted the barrier as its cause, considers it a success that the board has merely allowed a feasibility study, for which various private and public donors have raised $ 2 million. Mel Blaustein, a director at the foundation, has heard several arguments against a barrier over the years-too ugly, too expensive, and so forth--but the most persistent has been that people would simply kill themselves somewhere else, so why bother.'? This is nonsense, he says, "Most suicides are impulsive and preventable." A bridge without a barrier, adds Pat Hines, Kevin's father, is "like leaving a loaded gun in the psychiatric ward./

单选题The word "fallacy" (Line 3, Paragraph 1 ) most probably means

单选题Which of the following statements about the relationship between television and its viewers can best be inferred from the passage?

单选题It can be inferred from the text that American history textbooks used to assert that