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    本题由lindy提供
1992次学习

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. 


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答案:
C
首先要找到
最后一段那个实验作者的结论是什么,是“This method allows for effective control of nuisance algae while leaving solar ponds as one of the cleanest technologies providing energy for human use”这个论点可供攻击的点是“清洁”和“有效”。注意题目问的是削弱。 (A)沉入底部的藻类细胞只有经过24小时后才能被破坏。从“有效”方面攻击。但是24小时这个时间并不影响这个方法的有效性。 (B)沉入底部的藻类细胞的横向移动能力没有被损坏。从“有效”方面攻击。但是横向移动能力不影响细胞下沉,同时也不影响它被破坏。 (C)Correct. 稀释人工太阳能池的水中含有杀死水藻的微生物。两方面攻击,“清洁”方面有微生物不知道是否能保持死海的清洁。“有效”方面我们无从得知究竟是作者说的原因还是这些微生物杀死了藻类细胞。 (D)沉入底部的藻类细胞其实是被骤变的压力所杀死的。这个选项较易误选。注意这个选项并不能严重的削弱作者的结论。作者的结论是有效的杀死和清洁。该选项不反驳其中任何一点,只是作者说的消灭机理有问题。 (E)更高的盐度带来通过蒸发引起的上层水的透明度上升。该选项和作者的结论无关。

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