- 相干保举
2017年下半年大众英语四级专题摹拟操练
不知则问，不能则学，虽能不让，而后为德。闻之不见，虽博必谬;见之而不知，虽识不妄;知之而不行，虽敦必困。以下是小编为大师搜刮清算的2017年下半年大众英语四级专题摹拟操练，但愿对正在存眷的您有所赞助!更多出色内容请实时存眷咱们应届毕业生测验网!
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
剖析：
1.C
本文的标题问题是When was helium in the University formed?按照标题问题并连系文章的内容，咱们能够判定，本文首要先容的是氦元素是什么时辰在宇宙中构成的。
2.A
在第一段中咱们晓得：宇宙中除氢和氦的数目比拟多以外，别的元素的数目都很少。并且，氢在宇宙元素总量中占75%，以是氦元素在宇宙中必然是占第二位，仅次于氦。
3.A
文章第二段中先容了很多包罗氦的物资，包罗in old stars, in relatively young ones, in interstellar gas, and in the distant objects known as quasars同时作者还提到了宇宙射线，并告知咱们宇宙射线中也包罗氦。是以，作者在这里也提到了cosmic rays的目标是要令人们晓得别的一种包罗氦的物资，详细而言，便是说宇宙射线也是浩繁包罗氦元素的物资中的一局部。
4.B
第三段开首有如许一句话：In fact, nuclear reactions that convert hydrogen to helium are responsible for most of the energy that stars produce. 这句话的意义是，星体发生的大都能量来历与巴氢改变为氦的原子核反映。也便是说，星体上的氢改变为氦的.原子核反映发生了能量，这与选项A中的“星体中的氦的缔造进程中发生了能量”是一致的。
5.B
文章的开端有如许一句话：But the nuclear reactions that led to the formation of helium went on for only a relatively short time. 这句话的意义是，可是由于致使氦构成的原子核反映延续的时辰绝对较短。文章在最初指出，在宇宙构成的初期，氦并不存在，由于当时的温度太高。厥后跟着温度逐步下降，中子和质子才得以粘在一路。原子核反映构成了氦，但这一进程遏制的时辰很短。到了the universe was a few minutes old的时辰，氦的出产就遏制了。
【下半年大众英语四级专题摹拟操练】相干文章：
2017大众英语四级测验摹拟操练09-26
2017大众英语四级浏览指点摹拟操练09-04
2017年大众英语四级摹拟操练试题06-19
2017大众英语四级完型填空摹拟操练10-30
2024下半年英语四级浏览摹拟操练06-27
2017大众英语四级测验疾速浏览专题操练08-31
2016下半年英语四级浏览懂得摹拟操练10-02
2016下半年大众英语四级专项试题及谜底07-14
2017下半年大众英语四级测验温习试题10-27