2.语境意义题：

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　　Simulations of air, soil and water contamination on computer are increasingly being hailed as cheap and efficient ways of studying the environment. And as recent findings regarding the Chesapeake Bay indicate, computers can demonstrate complex interactions that simply cannot be determined using other methods.

　　Computer modeling has revealed that approximately 25 percent of the nitrogen in the Chesapeake comes from air pollution wafting in from as far away as western Pennsylvania, Ohio and Kentucky. (1) _______________

　　To arrive at this conclusion, Robin Dennis of the Environmental Protection Agency and his colleagues digitally recreated the atmosphere above the eastern U.S. and combined this information with another model that examined how water flows into the Chesapeake. In particular, the group simulated how air moves across the country and how nitrogen pollution reacts with other airborne compounds and then drops to the ground directly or in rain.

　　Conventional wisdom has generally held that nitrogen pollution falls out fairly ~ quickly. Thus, simple models had suggested that air pollution from local sources probably contributed to the bay's condition. (2) ______________

　　Although water testing helps to monitor the state of the bay, models demonstrate how the pollution gets there. Despite several years of regulations on waterborne pollution, nitrogen levels have not decreased as much as expected. (3) _______________

　　Much of the Chesapeake modeling was carried out at the EPA' s three-year-old National Environmental Supercomputing Center, which currently provides computer time for about 40 different projects on topics such as urban air pollution or the effects of landfills. Instead of having to sample a huge region to determine where a toxic compound might end up if released by a factory, researchers using computers need only am few samples to establish original conditions. (4) _______________

　　Such techniques can often save a great deal of money. In the early 1980s, researchers assessing the feasibility of a field experiment to study acid rain in the eastern U.S. -- a project similar in scale to one that might test the findings from the Chesapeake model put the price tag at $ 500 million. In contrast, Dennis estimates that the project to model the air pollution affecting the bay has cost around $ 500 000.

　　Yet for all their power, models cannot include every aspect of a natural system. (5) _______________ For instance, predictions about global warming have been controversial, because, as critics point out, various models, each with district assumptions, can give vastly different results. Having absolute faith in a simulation of an environmental problem can be tough, even for computer experts. Stephen E. Cabaniss of Kent University emphasize that for now, old-fashioned laboratory experiments as well as actual sampling of water, soil and air are still vital pieces of information needed to validate computer data to or nudge models in the right direction.

　　A And although experiments also cannot evaluate every detail, models in particular trigger complaints about accuracy.

　　B If people will not believe a computer model that forecasts a rise in global temperature over the next century, it is unclear whether they will accept a computer's assessment of what is safe to put in drinking water.

　　C Then, intricate computer programs, which consider details down to the movement of atoms, fill in aspects such as how a compound will degrade in the environment, whether any secondary products will be toxic, how the chemicals might percolate down to the water table or how they might accumulate in wildlife. In some cases, the toxic compound being studied may not have been produced yet.

　　D. Dennis asserts that although controls on water pollution must not be abandoned, attempts to lower nitrogen levels in the bay may not be fully successful unless air pollution is also reduced.

　　E But the more extensive model revealed that such pollution presents a much larger problem: 25 percent of nitrogen pollution is still being carried aloft 500 miles from its source.

　　F Don' t put away those lab coats yet.

　　G This finding alters the current perception that the bay' s greatest problems stem from more local waterborne pollution, such as sewage and runoff from agriculture.