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  3. Rain is not what it used to be. A new study reveals that much of the precipitation in Europe contains such high levels of dissol

Rain is not what it used to be. A new study reveals that much of the precipitation in Europe contains such high levels of dissol

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问题     Rain is not what it used to be. A new study reveals that much of the precipitation in Europe contains such high levels of dissolved pesticides that it could be illegal to supply it as drinking water.
    Studies in Switzerland have found that rain is laced with toxic levels of atrazine, alachlor and other commonly used crop sprays. "Drinking water standards are regularly exceeded in rain," says Stephan Muller, a chemist at the Swiss Federal Institute for Environmental Science and Technology in Dubendorf. The chemicals appear to have evaporated from fields and become part of the clouds.
    Both the European Union and Switzerland have set a limit of 100 nanograms for any particular pesticide in a liter of drinking water. But, especially in the first minutes of a heavy storm, rain can contain much more than that.
    In a study to be published by Muller and his colleague Thomas Bucheli in Analytical Chemistry this summer, one sample of rainwater contained almost 4000 nanograms per liter of 2,4-dinitrophe-nol, a widely used pesticide. Previously, the authors had shown that in rain samples taken from 41 storms, nine contained more than 100 nanograms of atrazine per liter, one of them around 900 nanograms.
    In the latest study, the highest concentrations of pesticides turned up in the first rain after a long dry spell, particularly when local fields had recently been sprayed. Until now, scientists had assumed that the pesticides only infiltrated groundwater directly from fields.
    Muller warns that the growing practice of using rainwater that falls onto roofs to recharge underground water may be adding to the danger. This water often contains dissolved herbicides that had been added to roofing materials, such as bitumen sheets, to prevent vegetation growing. He suggests that the first flush of rain should be diverted into sewers to minimize the pollution of drinking water, which is not usually treated to remove these herbicides and pesticides.
Muller warns us not______.
选项 A、to tap groundwater for drinking water
B、to use such roofing materials as bitumen sheets
C、to let the first flush of rain recharge underground water
D、to divert the first flush of rain into sewers without removing its herbicides and pesticides
答案C
解析 末段第一句讲到Muller警告说利用降落的雨水这种做法会recharge(再次袭击)under-ground water，因而是很危险的。这也就是让大家不要采用这种做法使the first flush ofrain recharge underground water。
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