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’s 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 San us billions upon billions of nuclei 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 converted into helium 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, a form of electro- magnetic radiation like light and radio waves only of very 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. At 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 Farther 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.
   A simple magnifying glass, focusing the Sun’s rays, can scoarch, a piece of wood or set a scrap of paper on fire. Solar radiation can also be concentrated on a much larger scale. It can burn a hole through thick steel plate, for example, or simulate the thermal shock of a nuclear blast. It can, that is, with the help of a super reflector of the sort that has been set up by French scientists high in the Pyroness. The world’s largest solar furnace is a complex of nearly 20,000 mirrors. It can concentrate enough sunlight to create’temperatures in excess of 6000 degrees Fahrenheit.
   The furnace’s appearance is as spectacular as its power. Its glittering eight - story - high reflector towers over very old houses. Anchored against a concrete office and laboratory building, the huge reflector consists of nearly 9000 separate mirrors. For the furnace to operate, these small mirrors must be adjusted so that their light will meet exactly at a focal point 59 feet in front of the giant reflector.
Which sentence proves that setting the giant reflector is a delicate operation?
选项 A、The first sentence in the last paragraph.
B、The second sentence in the last paragraph.
C、The last sentence in the last paragraph.
D、The last sentence in the third paragraph.
答案C
解析 这个问题涉及到两个方面即组成这个装置需要很多镜面而且它们放置的角度必须合适，使它们的光线能在这个巨大的反射装置前59英尺汇聚成一点。相比较而言，后者对整个装置的运转是非常关键的。而且最后一句话提到一个目的状语“For the furnace to operate”，因此应选择C。
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