Solar ponds are bodies of water in which circulation is incomplete and there is a very high salt concentration that increases with depth. This vertical change in salinity serves to trap heat because concentrated brine in the lowest water level acts as a collector and storage area for solar heat, while the less saline, lighter water at the upper levels provides insulation. Heat is thus retained in the depths.
An artificial pond of this type has been constructed on the western shore of the Dead Sea in Israel in order to test its suitability as a source of low-grade heat for conversion into electricity. An immediate threat to the success of the venture was the growth of algae. Water in solar ponds must be kept maximally transparent to allow penetration of light to the deep storage area. Therefore, any particles of matter in the water, such as algae cells, that scatter or absorb light will interfere with the collection of heat.
One proposed method of controlling the algae was the application of an algicide. However, the Dead Sea is a closed body of water without any outlet and as such is very easily contaminated. Extensive use of chemicals in numerous future full-scale solar ponds would lead to such contamination of the Dead Sea, which now enjoys a lucrative tourist trade.
A recent experiment has supplied a more promising method for controlling the algae. To repress the algae cells' capacity for accommodating themselves to environmental changes, the water in the solar pond was first made more saline through evaporation and then diluted by a rapid inflow of fresh water. This shock reduced the cells' ability to regulate the movement of water through their membranes. They rapidly absorbed water, resulting in distortions of shape, increase in volume, and impairment to motility. Their buoyancy adversely affected, the cells sank to the bottom of the pond, where they encountered the hot waters of the storage layer and were destroyed. This method allows for effective control of nuisance algae while leaving solar ponds as one of the cleanest technologies providing energy for human use.
Which of the following, if true, would seriously undermine the validity of the conclusions drawn from the experiment described in the last paragraph of the passage?
(A) The algae cells that sank to the bottom of the pond were destroyed only after a time lag of twenty-four hours.
(B) The lateral motility of the algae cells that sank to the bottom of the pond was not impaired.
(C) The water with which the artificial solar pond was diluted contained microorganisms that kill algae.
(D) The algae cells that sank to the bottom of the pond were actually killed by the rapid change in pressure.
(E) The higher salinity brought about through evaporation increased the transparency of the upper levels of water in the pond.
ANS:C
应该定位在最后一段，我选到B了……作者: sbjqbS 时间: 2010-9-13 06:34
我也错了选了B
However, the Dead Sea is a closed body of water without any outlet and as such is very easily contaminated. 上一段说这个死海without any outlet。
C选项说用来dilute的水里面有微生物，这样就是引入了其他的生物。
题里问的是undermine the validity of the conclusions drawn from the experiment described in the last paragraph of the passage：这个conclustion就是最后一句话：This method allows for effective control of nuisance algae while leaving solar ponds as one of the cleanest technologies providing energy for human use.这个方法能控制海藻同时能保证solar pounds是最清洁的能源，引入微生物不能保证其清洁性，因此错。
- Dilute the pond by a rapid inflow of fresh water
- Algae rapidly absorbed water--> distortions of shape, increase in volume, and impairment to motility.
-->Algae's buoyancy adversely affected, the cells sank to the bottom of the pond, where they encountered the hot waters of the storage layer and were destroyed.
The conclusion: "This method allows for effective control of nuisance algae while leaving solar ponds as one of the cleanest technologies providing energy for human use"
If the algae is killed by microorganisms: Algae are dead but their buoyancy is not affected. They do not sink to the storage layer. The dead cells are still floating in the higher layer, preventing "the penetration of light to the deep storage area"
--> undermine the above conclusion.
From Manhattan~~
解释的很详细~~难！！作者: liexodus 时间: 2010-9-14 20:11
其实这个不难，没有必要分析的那么详细。
这个实验主要是为了杀死algae，而同时实现while leaving solar ponds as one of the cleanest technologies providing energy for human use.
所以如果削弱的话，就看有没有他因就可以了，如果进一步的话，看这个他因是否会破坏cleanest 这个前提。
(A) The algae cells that sank to the bottom of the pond were destroyed only after a time lag of twenty-four hours. 不管什么时候死，只要死了就好！ 不削弱！
(B) The lateral motility of the algae cells that sank to the bottom of the pond was not impaired. 管他怎么动，要的是他死！不死不削弱！
(C) The water with which the artificial solar pond was diluted contained microorganisms that kill algae. 死了！
(D) The algae cells that sank to the bottom of the pond were actually killed by the rapid change in pressure. 死亡的原因，不削弱结论！
(E) The higher salinity brought about through evaporation increased the transparency of the upper levels of water in the pond. 完全无关，transparency 而且是上层的 和结论无权无关，迷惑项！
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