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标题: gwd-04-36 [打印本页]

作者: linmonkey 时间: 2004-11-7 23:24
标题: gwd-04-36

Q35 to Q37:

In addition to conventional

galaxies, the universe contains

very dim galaxies that until

Line recently went unnoticed by

(5) astronomers. ossibly as

numerous as conventional gal-

axies, these galaxies have the

same general shape and even

the same approximate number

(10) of stars as a common type of

conventional galaxy, the spiral,

but tend to be much larger.

Because these galaxies’

mass is spread out over

(15) larger areas, they have far

fewer stars per unit volume

than do conventional galaxies.

Apparently these low-surface-

brightness galaxies, as they

(20) are called, take much longer

than conventional galaxies to

condense their primordial gas

and convert it to stars—that is,

they evolve much more slowly.

(25) These galaxies may

constitute an answer to the long-

standing puzzle of the missing

baryonic mass in the universe.

Baryons—subatomic particles

(30) that are generally protons or

neutrons—are the source of

stellar, and therefore galactic,

luminosity, and so their numbers

can be estimated based on how

(35) luminous galaxies are. How-

ever, the amount of helium

in the universe, as measured

by spectroscopy, suggests

that there are far more baryons

(40) in the universe than estimates

based on galactic luminosity

indicate. Astronomers have

long speculated that the missing

baryonic mass might eventually

(45) be discovered in intergalactic

space or as some large popu-

lation of galaxies that are difficult

to detect.

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Q35:

The primary purpose of the passage is to

describe a phenomenon and consider its scientific significance

contrast two phenomena and discuss a puzzling difference between them

identify a newly discovered phenomenon and explain its origins

compare two classes of objects and discuss the physical properties of each

discuss a discovery and point out its inconsistency with existing theory

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Q36:

The author mentions the fact that baryons are the source of stars’ luminosity primarily in order to explain

how astronomers determine that some galaxies contain fewer stars per unit volume than do others

how astronomers are able to calculate the total luminosity of a galaxy

why astronomers can use galactic luminosity to estimate baryonic mass

why astronomers’ estimates of baryonic mass based on galactic luminosity are more reliable than those based on spectroscopic studies of helium

how astronomers know bright galaxies contain more baryons than do dim galaxies

the key is c, but i choose b,why???

作者: linmonkey 时间: 2004-11-10 23:10
谁帮我看看这题吧，谢谢了～～～～～

作者: wangyu73cn 时间: 2004-11-11 12:43

帮你顶一下。不知这里有没有你的问题答案，供参考：

http://forum.chasedream.com/dispbbs.asp?boardID=25&ID=56774&page=1

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