请教Prep-2-4-15

Essay #4.  156      (21764-!-item-!-188;#058&00156-00)

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.

Question #15.  156-08  (21948-!-item-!-188;#058&000156-08)

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.

 答案是C,D为什么不对呢？我觉得C和D差不多。

谢谢！

頂

I can't understand the connection of choice C and the article.

help!

同问

试着说说吧,这题确实挺难的.

D项不管是温度还是压力给搞死的, 好歹是水自己把algae搞定的, 应该都不能undermine the validity of the conclusion.

但是如果是有微生物冲进来,把algae都吃了,那情况就不一样了.原文说algae讨厌就讨厌在Therefore, any particles of matter in the water, such as algae cells, that scatter or absorb light will interfere with the collection of heat.那么现在的微生物进来了自然也会有同样的效果, 这就好像一个黑帮搞掉了另一个黑帮, 换汤不换药, 老百姓还是倒霉. 但是要是老百姓把黑帮都打死了, 或者都饿死了(比如开店的都不交保护费哈), 那黑帮就彻底垮了. 我这个例子举的有点搞哈,大家放松一下

這題一開始也寫錯了, 想了一下之後覺得(C)還蠻有道理的

題目說要weaken the conclusions drawn from the experiment, 先看一下experiment的原理是什麼

最後一段的the water in the solar pond was first made more saline through evaporation and then diluted by a rapid inflow of fresh water

如果這兩個步驟出了差錯,那麼整個實驗結果就會受到影響

(C)很明顯是發生在第二個步驟,如果用來稀釋的水裡面含有microorganism,即使algae死了,但是microorganism卻變成另一個阻礙吸收太陽能的因素

C是反对了cleanest的说法.

本来是让A自生自灭,但是C中又有别的东西来觉和,所以WEAKEN

open to discuss