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【C1】______at the Sun’s ver

A summary of the physical and chemical nature of life must begin, not on the Earth, but in the Sun; in【C1】______at the Sun’s ver

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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【C1】______at the Sun’s very center. It is here that is to be found the【C2】______of the energy that the Sun pours out into space is【C3】______The energy takes the form of light and heat. This energy is【C4】______at the center of the Sun as billions【C5】______billions of nuclei of hydrogen atoms【C6】______with each other and fuse together to form nuclei of helium, and in doing so,【C7】______some of the energy that is【C8】______in the nuclei of atoms. The【C9】______of light and heat of the Sun【C10】______that some 600 million tons of hydrogen be【C11】______into helium(氦)in the Sun every second. This the Sun has been doing for several thousands of millions of years. The nuclear energy is released at the Sun’s center as high-energy gamma radiation,【C12】______of electromagnetic radiation like light and radio waves, only of very much shorter【C13】______. This gamma radiation is absorbed by atoms inside the Sun to be【C14】______at slightly longer  wavelengths. This radiation, in its【C15】______is absorbed and reemitted. As the energy filters through the【C16】______of the solar interior, it passes through the X-ray part of the spectrum【C17】______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【C18】______of the Sun’s light and heat is emitted in such directions that【C19】______passing  unhindered through interplanetary space, it【C20】______the Earth.
【C19】
选项 A、while
B、as
C、before
D、after
答案D
解析 连词辨义题。该处意在说明“未被阻挡的能量穿越星空，最终到达地球”。其动作发生先后顺序必然是，穿越星空在前，到达地球在后，故应选择after。while和as都有“当……的时候”，但该处两动作并不同步；before将两动作先后顺序颠倒，故排除。
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