問題詳情

Passage 2: Questions 31-40To improve the productivity of land, farmers in developed countries use enormous quantities ofartificially produced nitrates as agricultural fertilizers. There is now growing evidence that these__(31)__ nitrates are overloading the natural system. __(32)__ they can be broken down orconverted into atmospheric nitrogen, they are often leached out of the soil by rain. These dissolvednitrates are often carried into streams and river systems, and down into ground water. This is thetime when nourishment can mean death. In some places, water for domestic use contains __(33)__high concentrations of nitrates that it exceeds safety levels for human consumption. Excessivequantities of nitrates reaching the water system can cause an algal bloom, a sudden and dramatic__(34)__ in the populations of algae, which use up the oxygen in the water. This change __(35)__leads to death of much of the life in the lake.To cope with such danger, people may need to work with nature. In the world’s tropicalregions, __(36)__ the temperature is generally high, the bacteria that cause denitrification canthrive. They can impoverish the soil and the plant life by __(37)__ the nitrates very quickly. Thepaddy field system overcomes this __(38)__ by waterlogging soil and slowing down the action ofthe denitrifying bacteria. Flooded fields also support the growth of blue-green algae, which are ableto __(39)__ nitrogen from the atmosphere into nitrogen compounds, making it available to thegrowing crop. __(40)__, farmers in the tropics have been able to use land productively, maintainingthe fertility of the soil under the difficult conditions at these latitudes.
31.
(A) exceptional
(B) original
(C) conventional
(D) additional
(E) partial

參考答案

答案：D
難度：簡單0.75
統計：A(2),B(1),C(1),D(12),E(0)

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