新GRE逻辑阅读 每日一练27

　　编辑点评： GRE阅读考试的材料，非常强调逻辑的关系，所以逻辑要点是大家在解GRE阅读题的时候的关键，本文就为大家例举了这样一篇逻辑短文，供大家参考和练习。

　　随着GRE阅读考试的难度日益增加，大家需要有针对性地进行练习，本文为大家例举的就是逻辑短文的练习，文末还附有答案，供大家更好地练习。

　　The deep sea typically has a sparse fauna dominated by tiny worms and crustaceans, with an even sparser distribution of larger animals. However, near hydrothermal vents, areas of the ocean where warm water 5 emerges from subterranean sources, live remarkable densities of huge clams, blind crabs, and fish.

　　Most deep-sea faunas rely for food on particulate matter,ultimately derived from photosynthesis, falling from above. The food supplies necessary to sustain the 10 large vent communities, however, must be many times the ordinary fallout. The first reports describing vent faunas proposed two possible sources of nutrition: bacterial chemosynthesis, production of food by bacteria using energy derived from chemical changes, and 15 advection, the drifting of food materials from surrounding regions. Later, evidence in support of the idea of intense local chemosynthesis was accumulated: hydrogen sulfide was found in vent water; many vent-site bacteria were found to be capable of chemosynthesis; and extremely 20 large concentrations of bacteria were found in samples of vent water thought to be pure. This final observation seemed decisive. If such astonishing concentrations of bacteria were typical of vent outflow, then food within the vent would dwarf any contribution from advection. 25 Hence, the widely quoted conclusion was reached hat bacterial chemosynthesis provides the foundation for hydrothermal-vent food chains an exciting prospect because no other communities on Earth are independent of photosynthesis.

　　30 There are, however, certain difficulties with this interpretation. For example, some of the large sedentary organisms associated with vents are also found at ordinary deep-sea temperatures many meters from the nearest hydrothermal sources. This suggests that bacterial 35 chemosynthesis is not a sufficient source of nutrition for these creatures. Another difficulty is that similarly dense populations of large deep-sea animals have been found in the proximity of smokers vents where water emerges at temperatures up to 350 C. No bacteria can survive such 40 heat, and no bacteria were found there. Unless smokers are consistently located near more hospitable warm-water vents, chemosynthesis can account for only a fraction of the vent faunas. It is conceivable, however, that these large, sedentary organisms do in fact feed on bacteria that 45 grow in warm-water vents, rise in the vent water, and then rain in peripheral areas to nourish animals living some distance from the warm-water vents.

　　Nonetheless, advection is a more likely alternative food source. Research has demonstrated that advective 50 flow, which originates near the surface of the ocean where suspended particulate matter accumulates,transports some of that matter and water to the vents.Estimates suggest that for every cubic meter of vent discharge, 350 milligrams of particulate organic 55 material would be advected into the vent area. Thus, for an average-sized vent, advection could provide more than 30 kilograms of potential food per day. In addition, it is likely that small live animals in the advected water might be killed or stunned by thermal and/or chemical 60 shock, thereby contributing to the food supply of vents.

　　For the following question, consider each of the choices separately and select all that apply

　　5. The passage provides information for answering which of the following questions EXCEPT?

　　□A What causes warm-water vents to form?

　　□B What role does hydrogen sulfide play in chemosynthesis?

　　□C Do bacteria live in the vent water of smokers?

　　6. The information in the passage suggests that the majority of deep-sea faunas that live in nonvent habitats have which of the following characteristics?

　　They do not normally feed on particles of food in the water.

　　They are smaller than many vent faunas.

　　They are predators.

　　They derive nutrition from a chemosynthetic food source.

　　They congregate around a single main food source.

　　7. Select the sentence in the passage in which the author implies that vents are colonized by some of the same animal found in other areas of the ocean floor, which might be a weakness for the bacterial chemosynthesis model.

　　8. The author refers to ―smokers‖ in the third paragraph most probably in order to

　　show how thermal shock can provide food for some vent faunas by stunning small animals

　　prove that the habitat of most deep-sea animals is limited to warm-water vents

　　explain how bacteria carry out chemosynthesis

　　demonstrate how advection compensates for the lack of food sources on the seafloor

　　present evidence that bacterial chemosynthesis may be an inadequate source of food for some vent faunas

　　答案：5. AB 6. B 7. For example, some of the large sedentary 8. E

　　上文的题目大家答对了几题?大家不仅要多做题，更要善于总结，这样才会有针对性地提高。