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Questions 12-20
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
Questions 21-30 In colonial America, people generally covered their beds with decorative13 quilts resembling those of the lands from which the quitters had come. Wealthy and socially prominent settlers made quilts of the English type, cut from large lengths of cloth of the same color and texture14 rather than stitched together from smaller pieces. They mad these until the advent15 of the Revolutionary War in I 775, when everything English came to be frowned upon.
Among the whole-cloth quilts made by these wealthy settlers during the early period are.
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1 astronomers | |
n.天文学者,天文学家( astronomer的名词复数 ) | |
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2 galaxy | |
n.星系;银河系;一群(杰出或著名的人物) | |
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3 galaxies | |
星系( galaxy的名词复数 ); 银河系; 一群(杰出或著名的人物) | |
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4 relatively | |
adv.比较...地,相对地 | |
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5 nuclei | |
n.核 | |
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6 constituents | |
n.选民( constituent的名词复数 );成分;构成部分;要素 | |
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7 remains | |
n.剩余物,残留物;遗体,遗迹 | |
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8 sufficiently | |
adv.足够地,充分地 | |
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9 neutrons | |
n.中子( neutron的名词复数 ) | |
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10 astronomical | |
adj.天文学的,(数字)极大的 | |
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11 by-product | |
n.副产品,附带产生的结果 | |
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12 determined | |
adj.坚定的;有决心的 | |
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13 decorative | |
adj.装饰的,可作装饰的 | |
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14 texture | |
n.(织物)质地;(材料)构造;结构;肌理 | |
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15 advent | |
n.(重要事件等的)到来,来临 | |
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