『新东方在线托福阅读』为托福考生准备了ETS托福TPO/Official 50 Passage 3阅读练习：Look at the four squares  that indicate where the following sentence could be added to the passage. Clearly, a more plausible mechanism was needed to explain how stars generate energy. Where would the sentence best fit? Click on a square  to add the sentence to the passage.真题题目及答案解析，TPO/Official 50 Passage 3阅读原文范文音频翻译

托福TPO/Official 50 Passage 3阅读原文Look at the four squares  that indicate where the following sentence could be added to the passage. Clearly, a more plausible mechanism was needed to explain how stars generate energy. Where would the sentence best fit? Click on a square  to add the sentence to the passage.题目答案及解析-新东方托福官方网校手机版

直到二十世纪中叶之前，科学家们一直认为恒星通过收缩来产生能量。

Until the early- to mid-twentieth century, scientists believed that stars generate energy by shrinking.

人们认为，随着恒星收缩，它们会越来越热，并在此过程中散发出光。

As stars contracted, it was thought, they would get hotter and hotter, giving off light in the process.

但是，这可能不是恒星发光的主要方式。

This could not be the primary way that stars shine, however.

如果是这样，它们将很少能持续一百万年，而不是我们所知道的数十亿年。

If it were, they would scarcely last a million years, rather than the billions of years in age that we know they are.

我们现在知道，核聚变为恒星提供了动力。

We now know that stars are fueled by nuclear fusion.

每次发生聚变时，能量会作为副产物释放。

Each time fusion takes place, energy is released as a by-product.

释放到太空中的能量就是我们所看到的星光。

This energy, expelled into space, is what we see as starlight.

当两个氢核粉碎在一起形成称为氘核的粒子（正质子和中子的组合）时，聚变过程开始。

The fusion process begins when two hydrogen nuclei smash together to form a particle called the deuteron (a combination of a positive proton and a neutral neutron).

氘核容易与其他质子结合形成氦。

Deuterons readily combine with additional protons to form helium.

反过来，氦可以融合在一起形成更重的元素，例如碳。

Helium, in turn, can fuse together to form heavier elements, such as carbon.

在一个典型的恒星中，合并之后还会发生合并，直到大量的重元素被积累为止。

In a typical star, merger after merger takes place until significant quantities of heavy elements are built up.

在这一点上，我们必须区分两种不同的恒星类型：I类恒星和II类恒星，后者比前者要大得多。

We must distinguish, at this point, between two different stellar types: Population I and Population II, the latter being much older than the former.

这些恒星群也可以通过其位置来区分。

These groups can also be distinguished by their locations.

我们的银河系的形状像一个围绕中央凸起的圆盘状。

Our galaxy, the Milky Way, is shaped like a flat disk surrounding a central bulge.

I类恒星主要存在于银河盘中，而II类恒星则大多位于银河系的中央凸起和该凸起周围的光晕中。

Whereas Population I stars are found mainly in the galactic disk, Population II stars mostly reside in the central bulge of the galaxy and in the halo surrounding this bulge.

II类恒星可以追溯到宇宙的早期。

Population II stars date to the early stages of the universe.

它们在宇宙充满氢气和氦气时形成，最初几乎不含重元素。

Formed when the cosmos was filled with hydrogen and helium gases, they initially contained virtually no heavy elements.

它们一直发光，直到可熔物质耗尽。

They shine until their fusible material is exhausted.

当II类恒星消亡时，它们的物质散布到太空中。

When Population II stars die, their material is spread out into space.

这些尘埃中的一部分最终被并入了新形成的I类恒星中。

Some of this dust is eventually incorporated into newly formed Population I stars.

尽管I类恒星主要由氢气和氦气组成，但它们也含有重元素（比氦重），占其质量的1％或2％。

Though Population I stars consist mostly of hydrogen and helium gas, they also contain heavy elements (heavier than helium), which comprise about 1 or 2 percent of their mass.

这些较重的物质是由恒星收集的较轻元素融合而成的。

These heavier materials are fused from the lighter elements that the stars have collected.

因此，I类恒星包含的物质曾经属于前几代恒星。

Thus, Population I stars contain material that once belonged to stars from previous generations.

太阳是I类恒星的一个很好的例子。

The Sun is a good example of a Population I star.

太阳消亡后会发生什么？在数十亿年中，我们的母星将燃烧得更加明亮。

What will happen when the Sun dies? In several billion years, our mother star will burn much brighter.

它将消耗越来越多的核燃料，直到原始氢所剩无几。

It will expend more and more of its nuclear fuel, until little is left of its original hydrogen.

然后，在不远的将来，太阳中心的所有核反应都将停止。

Then, at some point in the far future, all nuclear reactions in the Sun’s center will cease.

一旦太阳进入“后核”阶段，它将有效地分成两个不同的区域：内部区域和外部区域。

Once the Sun passes into its “postnuclear” phase, it will separate effectively into two different regions: an inner zone and an outer zone.

尽管内部区域中不再有氢燃料残留，但在外部区域中将有少量氢燃料残留。

While no more hydrogen fuel will remain in the inner zone, there will be a small amount left in the outer zone.

迅速地，变化将开始发生，这将使太阳分裂。

Rapidly, changes will begin to take place that will serve to tear the Sun apart.

内部区域，核火不再燃烧，将在其自身重量的影响下开始坍塌，并收缩成一个密密麻麻的微小热核。

The inner zone, its nuclear fires no longer burning, will begin to collapse under the influence of its own weight and will contract into a tiny hot core, dense and dim.

相反的命运等待着外部区域——它将变成一个松散的气球体。

An opposite fate will await the outer region, a loosely held-together ball of gas.

内部区域收缩引起的冲击波将通过垂死的恒星发出涟漪，将恒星外部的物质推得越来越远。

A shock wave caused by the inner zone’s contraction will send ripples through the dying star, pushing the stellar exterior’s material farther and farther outward.

然后，外壳将迅速增长，并在短时间内增加数百倍的大小。

The outer envelope will then grow rapidly, increasing, in a short interval, hundreds of times in size.

随着它的扩展，它将冷却数千度。

As it expands, it will cool down by thousands of degrees.

最终，太阳将变成一颗清凉明亮的红色巨星。

Eventually, the Sun will become a red giant star, cool and bright.

它是如此之大，以至于将占据过去曾经是地球轨道的整个空间，而且它如此耀眼，以至可以用肉眼从数千光年以外的地方看到它。

It will be so large that it will occupy the whole space that used to be the Earth’s orbit and so brilliant that it would be able to be seen with the naked eye thousands of light-years away.

这种方式将存在数百万年，并将其外壳物质逐渐释放到太空中。

It will exist that way for millions of years, gradually releasing the material of its outer envelope into space.

最终，太阳的气态外层将一无所有。剩下的将是炙热的白色内核。

Finally, nothing will be left of the gaseous exterior of the Sun; all that will remain will be the hot, white core.

The Sun will have become a white dwarf star.

核心将收缩，释放出最后的能量，太阳将最终消亡。

The core will shrink, giving off the last of its energy, and the Sun will finally die.

The word “readily” in the passage is closest in meaning to

According to paragraph 1, the energy that comes from stars and that is seen as light is the result of

In paragraph 1, why does the author point out that stars are billions of years old?

According to paragraphs 2 and 3, all of the following are true of Population I stars EXCEPT:

Why does the author ask the question “What will happen when the Sun dies?”?

According to paragraph 5, once the Sun is in its “postnuclear” phase, the outer zone will differ from the inner zone in that the outer zone will

According to paragraph 5, which of the following will be true about the inner core of the dying Sun?

Paragraph 5 supports which of the following about the death of the Sun?

Look at the four squares  that indicate where the following sentence could be added to the passage. Clearly, a more plausible mechanism was needed to explain how stars generate energy. Where would the sentence best fit? Click on a square  to add the sentence to the passage.

Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.

Star Death Until the early- to mid-twentieth century, scientists believed that stars generate energy by shrinking.  As stars contracted, it was thought, they would get hotter and hotter, giving off light in the process.  This could not be the primary way that stars shine, however.  If it were, they would scarcely last a million years, rather than the billions of years in age that we know they are.  We now know that stars are fueled by nuclear fusion. Each time fusion takes place, energy is released as a by-product. This energy, expelled into space, is what we see as starlight. The fusion process begins when two hydrogen nuclei smash together to form a particle called the deuteron (a combination of a positive proton and a neutral neutron). Deuterons readily combine with additional protons to form helium. Helium, in turn, can fuse together to form heavier elements, such as carbon. In a typical star, merger after merger takes place until significant quantities of heavy elements are built up. We must distinguish, at this point, between two different stellar types: Population I and Population II, the latter being much older than the former. These groups can also be distinguished by their locations. Our galaxy, the Milky Way, is shaped like a flat disk surrounding a central bulge. Whereas Population I stars are found mainly in the galactic disk, Population II stars mostly reside in the central bulge of the galaxy and in the halo surrounding this bulge. Population II stars date to the early stages of the universe. Formed when the cosmos was filled with hydrogen and helium gases, they initially contained virtually no heavy elements. They shine until their fusible material is exhausted. When Population II stars die, their material is spread out into space. Some of this dust is eventually incorporated into newly formed Population I stars. Though Population I stars consist mostly of hydrogen and helium gas, they also contain heavy elements (heavier than helium), which comprise about 1 or 2 percent of their mass. These heavier materials are fused from the lighter elements that the stars have collected. Thus, Population I stars contain material that once belonged to stars from previous generations. The Sun is a good example of a Population I star. What will happen when the Sun dies? In several billion years, our mother star will burn much brighter. It will expend more and more of its nuclear fuel, until little is left of its original hydrogen. Then, at some point in the far future, all nuclear reactions in the Sun’s center will cease. Once the Sun passes into its “postnuclear” phase, it will separate effectively into two different regions: an inner zone and an outer zone. While no more hydrogen fuel will remain in the inner zone, there will be a small amount left in the outer zone. Rapidly, changes will begin to take place that will serve to tear the Sun apart. The inner zone, its nuclear fires no longer burning, will begin to collapse under the influence of its own weight and will contract into a tiny hot core, dense and dim. An opposite fate will await the outer region, a loosely held-together ball of gas. A shock wave caused by the inner zone’s contraction will send ripples through the dying star, pushing the stellar exterior’s material farther and farther outward. The outer envelope will then grow rapidly, increasing, in a short interval, hundreds of times in size. As it expands, it will cool down by thousands of degrees. Eventually, the Sun will become a red giant star, cool and bright. It will be so large that it will occupy the whole space that used to be the Earth’s orbit and so brilliant that it would be able to be seen with the naked eye thousands of light-years away. It will exist that way for millions of years, gradually releasing the material of its outer envelope into space. Finally, nothing will be left of the gaseous exterior of the Sun; all that will remain will be the hot, white core. The Sun will have become a white dwarf star. The core will shrink, giving off the last of its energy, and the Sun will finally die.