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[问答] GRE阅读求助一题 [复制链接]

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发表于 2012-1-15 22:44:12 |只看该作者 |倒序浏览

本帖最后由留学2013 于 2012-1-15 22:45 编辑

陈虎平36套第11套第6题
The information in the passage suggests thatthe majority of deep-sea faunas that live in nonvent habitats have which of thefollowing characteristics?.(L14——15 The food supplies necessary
to sustain the large vent communities, B直接对应)
A. They do not normally feed onparticles of food in the water.
B.They are smaller than many vent faunas
C. They are predators.
D. They derive nutrition from achemosynthetic food source.
E. They congregate around asingle main food source.
答案：(B)

原文：Thedeep sea typically has a sparse

fauna dominated by tiny worms and

(5) crustaceans, with an even sparser

distribution of larger animals. However,

near hydrothermal vents, areas of the

ocean where warm wateremerges from

subterranean sources,live remarkable
(10) densities of huge clams, blind crabs,

and fish. Most deep-sea faunasrely for

food on particulate matter, ultimately

derived from photosynthesis, falling

from above. The food supplies necessary
(15)to sustain the large vent communities,

however, must be many times the

ordinary fallout. The first reports

describing vent faunas proposed two

possible sources of nutrition: bacterial

(20)chemosynthesis, production of food by

bacteria using energy derived from

chemical changes, and advection,the

drifting of food materials from

surrounding regions. Later,evidence in

(25) support of the idea of intense local

chemosynthesis wasaccumulated:

hydrogen sulfied was found in vent

water; many vent-site bacteria were

found to be capable of chemosynthesis;
(30)and extremely large concentrations of

bacteria were found in samples of vent

water thought to be pure.This final

observation seemeddecisive. If such

astonishing concentrations ofbacteria
(35) were typical of ventoutflow, then
food within the vent would dwarfany
contribution from advection.Hence,
the widely quoted conclusion was
reached that bacterialchemosynthesis
(40) provides the foundation for
hydrothermal- vent food chains—an
exciting prospect because noother
communities on Earth areindependent
of photosynthesis.
(45)
There are, however, certaindifficul-

ties with thisinterpretation.For example,

some of the large sedentary organisms

associated with vents are alsofound at

ordinary deep-sea temperaturesmany
(50)meters from the nearest hydrothermal

sources. This suggests thatbacterial

chemosynthesis is not asufficient

source of nutrition for thesecreatures.

Another difficulty is thatsimilarly

(55)dense populations of large deep-sea

animals have been found in the

proximity of "smokers"–ventswhere

water emerges at temperatures upto

350°C. No bacteria can survivesuch
(60)heat, and no bacteria were found there.

Unless smokers are consistently

located near more hospitablewarm-water

vents, chemosynthesis can accountfor

only a fraction of thevent faunas.

(65)It is conceivable, however, that

these large, sedentary organismsdo

in fact feed on bacteria thatgrow in

warm-water vents, rise in the vent

water, and then rain inperipheral areas
(70)to nourish animals living some distance

from the warm-water vents.
　　
Nonethelessadvection is a more likely

alternative foodsource. Researchhas

demonstrated that advective flow,which
(75)originates near the surface of the ocean

where suspended particulatematter

accumulates, transports some ofthat

matter and water to the vents.Estimates

suggest that matter and water tothe
(80)vents. Estimates suggest that for every

cubic meter of vent discharge,

milligrams of particulateorganic

material would be advected intothe

vent area. Thus, for anaverage-sized
(85)vent, advection could provide more

than 30kilograms of potential food per

day. In addition, it is likelythat small

live animals in the advectedwater might

be killed or stunned by thermaland/or
(90)chemical shock, thereby contributing to
the food supply of vents.

我选的是C，我的根据是这句话：“ It is conceivable, however, that
> <

these large, sedentary organisms do

in fact feed on bacteria that grow in

warm-water vents, rise in the vent

water, and then rain in peripheral areas
(70) to nourish animals living some distance
　　from the warm-water vents.”
好心人指点一下嘛

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沙发

发表于 2012-1-15 23:15:15 |只看该作者

可以先检索一下前辈们的解释。

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发表于 2012-1-16 09:02:31 |只看该作者

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