首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
医学
The elements other than hydrogen and helium exist in such small quantities that it is accurate to say that the universe is somew
The elements other than hydrogen and helium exist in such small quantities that it is accurate to say that the universe is somew
admin
2013-12-06
23
问题
The elements other than hydrogen and helium exist in such small quantities that it is accurate to say that the universe is somewhat more than 75 percent hydrogen.
Astronomers have measured the abundance of helium throughout our galaxy and in other galaxies as well. Helium has been found in old stars, in relatively young ones, in interstellar gas, and in the distant objects known as quasars. Helium nuclei have also been found to be constituents of cosmic rays that fall on the earth(cosmic "rays" are not really a form of radiation; they consist of rapidly moving particles of numerous different kinds). It doesn’t seem to make very much difference where the helium is found. Its relative abundance never seems to vary much. In some places, there may be slightly more of it; in others, slightly less, but the ratio of helium to hydrogen nuclei always remains about the same.
Helium is created in stars. In fact, nuclear reactions that convert hydrogen to helium are responsible for most of the energy that stars produce. However, the amount of helium that could have been produced in this manner can be calculated, and it turns out to be no more than a few percent. The universe has not existed long enough for this figure to be significantly greater. Consequently, if the universe is somewhat more than 25 percent helium now, then it must have been about 25 percent helium at a time near the beginning.
However, when the universe was less than one minute old, no helium could have existed. Calculations indicate that before this time temperatures were too high and particles of matter were moving around much too rapidly. It was only after the one-minute point that helium could exist. By this time, the universe had cooled sufficiently that neutrons and protons could stick together. But the nuclear reactions that led to the formation of helium went on for only a relatively short time. By the time the universe was a few minutes old, helium production had effectively ceased.
Why does the author mention "cosmic rays" in Paragraph 2?
选项
A、As part of a list of things containing helium.
B、As an example of an unsolved astronomical puzzle.
C、To explain how the universe began.
D、To explain the abundance of hydrogen in the universe.
答案
A
解析
文章第二段中介绍了许多包含氦的物质,包括in old stars,in relatively young ones,ininterstellar gas,and in the distant objects known as quasars,同时作者还提到了宇宙射线,并告诉我们宇宙射线中也包含氦。因此,作者在这里也提到了cosmic rays的目的是要使人们知道另外一种包含氦的物质,具体而言,就是说宇宙射线也是众多包含氦元素的物质中的一部分。
转载请注明原文地址:https://kaotiyun.com/show/svU3777K
本试题收录于:
医学博士外语题库考研分类
0
医学博士外语
考研
相关试题推荐
Sheisvery______,andwillbeabletoperformallrequiredtaskswell.
Ihadneverbeeninthepublicwardofahospitalbefore,anditwasmyfirstexperienceofdoctorswhohandleyouwithoutspeak
Exceptformother’smilk,nodrinkboastsamore______reputationforyoungstersthanfruitjuice.
TherewereredfacesatoneofBritain’sbiggestbanksrecently.Theyhadacceptedatelephoneordertobuy$100,000worthof
A、Shelearnedaforeignlanguage.B、ShelearnedtomakefriendsC、Shelearnedtobeateacher.D、Shelearnedlivingskills.D根据S
Personalizedgeneticdiagnosisandtherapysayyou’reyoungandhealthy,andyougoinforaroutinephysical.Yourdoctortake
Forseveralyears,scientistshavebeentestingasubstancecalledinterferon(干扰素),apotentialwonderdrugthatisprovingtob
Theelementsotherthanhydrogenandheliumexistinsuchsmallquantitiesthatitisaccuratetosaythattheuniverseissomew
Thebedhasbeen______inthefamily.Itwasmygreat-grandmother’soriginally.
A、Playtennis.B、Takeoutthetrash.C、Playcomputergames.D、Gotocourtforalawsuit.A细节题。男女双方将去playtennis,输的一方(loser)必须倒一
随机试题
王令诗歌的特点是什么?
价值规律在私有制商品经济中的作用是()
下列对于母乳喂养的优点叙述不正确的是()
工伤保险的基本原则有()。
李克强在国务院先进制造与3D打印专题讲座上强调,用新理念新技术推动中国制造由大变强。下列有关说法错误的是()。
简述解放战争时期人民解放军战略决战的条件和胜利的原因。
完成下列命令行,对网络接口进行地址初始化的配置:firewall(config)#ipaddressinside(1)(2)fnrewall(config)#ipaddressoutside(3)(4)如果使外部所有主机不能访问
从下列选项中选取合适的答案分别填入图4-1中的(1)~(4)处。A.DES算法B.MD5算法C.会话密钥D.数字证书E.甲的公钥F.甲的私钥G.乙的公钥H.乙的私钥当乙收到了地
NowmoreandmoreChinese,especiallytheyoung,havebeguntobuycarsorhousesonbankloan.Writeapassageofatleast120
WhatwasthemostimportantjobfortheastronautsofDiscovery?
最新回复
(
0
)