Reading Comprehension
part A
Read the following two texts. Answer the questions below each text by choosing A.B.C or D. When was helium in the University formed?
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 mater 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.
1.What does the passage mainly explain?
A.How stars produce energy.
B.The difference between helium and hydrogen.
C.When most of the helium in the universe hydrogen.
D.Why hydrogen is abundant.
2.According to the passage, helium is ____.
A.the second-most abundant element in the universe
B.difficult to detect
C.the oldest element in the universe
D.the most prevalent element in quasars
3.Why does the author mention “cosmic rays” in paragraph 2?
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.
4.The creation of helium within stars ____.
A.cannot be measured
B.produces energy
C.produces helium to be much more abundant in old stars than in young stars.
5.Most of the helium in the universe was formed _____.
A.in interstellar space
B.in a very short time
C.during the first minute of the universe’s existence
D.before most of the hydrogen
一级建造师二级建造师二级建造师造价工程师土建职称公路检测工程师建筑八大员注册建筑师二级造价师监理工程师咨询工程师房地产估价师 城乡规划师结构工程师岩土工程师安全工程师设备监理师环境影响评价土地登记代理公路造价师公路监理师化工工程师暖通工程师给排水工程师计量工程师
执业药师执业医师卫生资格考试卫生高级职称执业护士初级护师主管护师住院医师临床执业医师临床助理医师中医执业医师中医助理医师中西医医师中西医助理口腔执业医师口腔助理医师公共卫生医师公卫助理医师实践技能内科主治医师外科主治医师中医内科主治儿科主治医师妇产科医师西药士/师中药士/师临床检验技师临床医学理论中医理论