GRE考试

【单选题】Given that 8 percent of food crops grows faster on farms using groundwater than the aquifers are replenished, and many large rivers are so heavily diverted that they do not reach the sea for much of the year, researchers believe freshwater sources--underground aquifers and rivers--are stresseD、Better management of soil and water and creative cropping patterns can boost production from rainfall-watered cropland, but the heaviest burden will fall on irrigated lanD、At present, most farmers irrigate their crops by channeling water down their fields in parallel furrows.　　One alternative, drip systems, enables farmers to deliver water directly to the plants’’ roots drop by drop, nearly eliminating waste by distributing water at low pressure through a network of perforated plastic tubing installed on or below the surface of the soil, where it then emerges through small holes at a slow but steady pace.Because the plants enjoy an ideal moisture environment, drip irrigation usually offers the added bonus of higher crop yields.Another alternative, sprinklers, can perform almost as well as drip methods when designed properly, but traditional high-pressure irrigation sprinklers spray water high into the air to cover as large a land area as possible, and the more time the water spends in the air, the more of it evaporates before use.　　Despite the payoffs, the higher costs of these technologies relative to simple flooding methods have been a barrier to their spread, and so has the prevalence of national water policies that discourage rather than foster efficient water use. Many governments have set very low prices for publicly supplied irrigation, leaving farmers with little motivation to invest in ways to conserve water or to improve efficiency and most authorities have also failed to regulate groundwater pumping, even in regions where aquifers are over-tappeD、Therefore, farmers might be inclined to conserve their own water supplies if they could profit from selling the surplus, but this practice is often discourageD、　　Efforts aside from irrigation technologies are also conducive to the reduction of agricultural demand for water; for instance, measurements of climate factors such as temperature and precipitation can be fed into a computer that calculates how much water a typical plant is consuming, and farmers can use this figure to determine, quite accurately, when and how much to irrigate their particular crops throughout the growing season.But the most effective, if unlikely way, to do more with less water is to reconfigure our diets, especially the typical NorthAmerican diet, which, with its large share of animal products, requires twice as much water as diets common in manyAsian and someEuropean countries.Eating lower on the food chain could allow the same volume of water to feed twoAmericans instead of one, and despite the resultant loss of nutrition, this may be the only recourse for countries serious about reducing their aquifer strain. The author regards the new means of water-use reduction under discussion as________.
A、wholly effective, but typically ignored
B．inexpensive, but insufficiently useful
C．promising, but difficult to implement
D．necessary, but likely to produce ill side-effects

E、universally accessible, but unnecessary

网考网参考答案：C
网考网解析：
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