2. 外语
  3. A summary of the physical and chemical nature of life must begin, not on the Earth, but in the Sun; in fact, at the Sun’s very c

A summary of the physical and chemical nature of life must begin, not on the Earth, but in the Sun; in fact, at the Sun’s very c

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问题     A summary of the physical and chemical nature of life must begin, not on the Earth, but in the Sun; in fact, at the Sun’s very center. It is here that is to be found the source of the energy that the Sun constantly pours out into space as light and heat. This energy is liberated at the center of the Sun as billions upon billions of nuclei of hydrogen atoms collide with each other and fuse together to form nuclei of helium, and, in doing so, release some of the energy that is stored in the nuclei of atoms. The output of light and heat of the Sun requires that some 600 million tons of hydrogen be converts into helium in the Sun every second. This the Sun has been doing thousands of millions of years.
    The nuclear energy is released at the Sun’s center as high-energy gamma radiation, a form of electro magnetic radiation like light as radio waves, only of every much shorter wavelength. This gamma radiation is absorbed by atoms inside the Sun, to be reemitted at slightly longer wavelengths. This radiation, in its turn, is absorbed and reemitted. As the energy filters through the layers of the solar interior, it passes through the x-ray part of the spectrum, eventually becoming light. At this stage, it has reached what we call the solar surface, and can escape into space, without being absorbed further by solar atoms. A very small fraction of the Sun’s light and heat is emitted in such directions that, after passing unhindered through interplanetary space, it hits the Earth.
What does the passage mainly discuss?
选项 A、The production of solar light and heat.
B、The physical and chemical nature of life.
C、The conversion of hydrogen to helium.
D、Radiation in the x-ray part of the spectrum.
答案A
解析 文章第一段讲：述太阳正中心是太阳不断发向宇宙的光和热的源泉，发出的光和热的能量的生成是大量氢原子相互碰撞产生的。第二段主要讲述核能如何变成光并到达地球。综合两段的内容可知，A项为正确，B项、C项、D项虽然文中也曾提到，但不是文章主题。
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