托福模拟试题：宇宙由什么元素组成

 　　The elements other than hydrogen and helium exist In such small quantities that it is accurate to say that the universe somewhat more than 25 percent helium by weight and somewhat less than 25 percent hydrogen.

　　Astronomers¹ have measured the abundance of helium throughout our galaxy² and in other galaxies³ as well. Helium has been found In old stars, in relatively⁴ young ones, in interstellar gas, and in the distant objects known as quasars. Helium nuclei⁵ have also been found to be constituents⁶ 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 remains⁷ 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 he 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 sufficiently⁸ that neutrons⁹ 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.

　　12. 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 was formed(D)Why hydrogen is abundant

　　13. 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 quasars14. The word "constituents" in line 7 is closest in meaning to(A) relatives

　　(B) causes

　　(C)components

　　(D) targets

　　15. Why does the author mention "cosmic rays't' in line 7?

　　(A)As part of a list of things containing helium(B) As an example of an unsolved astronomical¹⁰ puzzle(C) To explain how the universe began

　　(D) To explain the abundance of hydrogen in the universe16. The word "vary" in line 10 is closest ill meaning to(A) mean

　　(B) stretch

　　(C) change

　　(D) include

　　17. The creation of helium within stars

　　(A) cannot be measured

　　(B) produces energy

　　(C) produces hydrogen as a by-product¹¹

　　(D) causes helium to be much more abundant In old stars than In young star:

　　18. The word "calculated" in line 15 is closest in meaning to(A) ignored

　　(B) converted

　　(C) increased

　　(D) determined¹²

　　19. 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

　　20. The word "ceased" in line 26 is closest in meaning to(A)extended

　　(B)performed

　　(C)taken hold

　　(D)stopped

 

1 astronomers   

n.天文学者，天文学家( astronomer的名词复数 )

参考例句：

• Astronomers can accurately foretell the date,time,and length of future eclipses. 天文学家能精确地预告未来日食月食的日期、时刻和时长。 来自《简明英汉词典》
• Astronomers used to ask why only Saturn has rings. 天文学家们过去一直感到奇怪，为什么只有土星有光环。 来自《简明英汉词典》

2 galaxy   

n.星系；银河系；一群(杰出或著名的人物)

参考例句：

• The earth is one of the planets in the Galaxy.地球是银河系中的星球之一。
• The company has a galaxy of talent.该公司拥有一批优秀的人才。

3 galaxies   

星系( galaxy的名词复数 )； 银河系； 一群（杰出或著名的人物）

参考例句：

• Quasars are the highly energetic cores of distant galaxies. 类星体是遥远星系的极为活跃的核心体。
• We still don't know how many galaxies there are in the universe. 我们还不知道宇宙中有多少个星系。

4 relatively   

adv.比较...地，相对地

参考例句：

• The rabbit is a relatively recent introduction in Australia.兔子是相对较新引入澳大利亚的物种。
• The operation was relatively painless.手术相对来说不痛。

5 nuclei   

n.核

参考例句：

• To free electrons, something has to make them whirl fast enough to break away from their nuclei. 为了释放电子，必须使电子高速旋转而足以摆脱原子核的束缚。
• Energy is released by the fission of atomic nuclei. 能量是由原子核分裂释放出来的。

6 constituents   

n.选民( constituent的名词复数 )；成分；构成部分；要素

参考例句：

• She has the full support of her constituents. 她得到本区选民的全力支持。
• Hydrogen and oxygen are the constituents of water. 氢和氧是水的主要成分。 来自《简明英汉词典》

7 remains   

n.剩余物，残留物；遗体，遗迹

参考例句：

• He ate the remains of food hungrily.他狼吞虎咽地吃剩余的食物。
• The remains of the meal were fed to the dog.残羹剩饭喂狗了。

8 sufficiently   

adv.足够地，充分地

参考例句：

• It turned out he had not insured the house sufficiently.原来他没有给房屋投足保险。
• The new policy was sufficiently elastic to accommodate both views.新政策充分灵活地适用两种观点。

9 neutrons   

n.中子( neutron的名词复数 )

参考例句：

• The neutrons and protons form the core of the atom. 中子和质子构成了原子核。 来自《简明英汉词典》
• When an atom of U235 is split,several neutrons are set free. 一个铀235原子分裂时，释放出几个中子。 来自《简明英汉词典》

10 astronomical   

adj.天文学的，（数字）极大的

参考例句：

• He was an expert on ancient Chinese astronomical literature.他是研究中国古代天文学文献的专家。
• Houses in the village are selling for astronomical prices.乡村的房价正在飙升。

11 by-product   

n.副产品，附带产生的结果

参考例句：

• Freedom is the by-product of economic surplus.自由是经济盈余的副产品。
• The raw material for the tyre is a by-product of petrol refining.制造轮胎的原材料是提炼汽油时产生的一种副产品。

12 determined   

adj.坚定的；有决心的

参考例句：

• I have determined on going to Tibet after graduation.我已决定毕业后去西藏。
• He determined to view the rooms behind the office.他决定查看一下办公室后面的房间。