名師講座

    ★ 名師團在線指導12月四六級聽力備考：付思遙

    ★ 名師團在線指導12月四六級詞匯備考：劉一男

    ★ 名師團在線指導12月四六級全項備考：趙建昆

    ★ 名師在線指導12月四六級最后沖刺：趙建昆 屠皓民

    ★ 視頻：名師王江濤指導四六級考試寫作最后提分
 

    沖刺備考

    ★ 考前必讀：六級考試寫作高分必殺100詞

    ★ 四六級名師指導：作文最后提分技巧

    ★ 四六級提分最高“性價比”：名師改作文

    ★ 六級考試寫作最后提分：常見強調手法

    ★ 12月四六級最后提分：寫作必備模板大全
 

2011四六級VIP全程班：早準備 早通關

　　20.The source of Energy

　　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 librated 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 converted into helium in the Sun every second. This the Sun has been doing for several thousands of millions of year.

　　The nuclear energy is released at the Sun’s center as high-energy gamma radiation, a form of electromagnetic 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. 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.

　　Vision

　　Human vision like that of other primates has evolved in an arboreal environment. In the dense complex world of a tropical forest, it is more important to see well that to develop an acute sense of smell. In the course of evolution members of the primate line have acquired large eyes while the snout has shrunk to give the eye an unimpeded view. Of mammals only humans and some primates enjoy color vision. The red flag is black to the bull. Horses live in a monochrome world .light visible to human eyes however occupies only a very narrow band in the whole electromagnetic spectrum. Ultraviolet rays are invisible to humans though ants and honeybees are sensitive to them. Humans though ants and honeybees are sensitive to them. Humans have no direct perception of infrared rays unlike the rattlesnake which has receptors tuned into wavelengths longer than 0.7 micron. The world would look eerily different if human eyes were sensitive to infrared radiation. Then instead of the darkness of night, we would be able to move easily in a strange shadowless world where objects glowed with varying degrees of intensity. But human eyes excel in other ways. They are in fact remarkably discerning in color gradation. The color sensitivity of normal human vision is rarely surpassed even by sophisticated technical devices.

最后沖刺:名師團在線指導12月四六級備考

四級歷年真題（2001-2009） 

2001年1月2001年6月2002年1月2002年6月2003年1月2003年6月2003年9月2004年1月2004年6月2005年1月2005年6月2005年12月2006年6月2006年12月2007年6月2007年12月2008年6月2008年12月2009年6月2009年12月

六級歷年真題（2001-2009）

2001年1月2001年6月2002年1月2002年6月2003年1月2003年6月 2003年9月2004年1月2004年6月2005年1月2005年6月2005年12月2006年6月2006年12月2007年6月2007年12月2008年6月2008年12月2009年6月2009年12月 

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