问答题 《复合题被拆开情况》 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 ishere where is to be found the source of the energy that the Sun constantly【S1】________pours out into the space as light and heat. This energy is liberated at the【S2】________center of the Sun as billions on billions of nuclei of hydrogen atoms【S3】________collide with each other and fuse together to form nuclei of helium, and,in doing so, releases some of the energy that is stored in the nuclei of【S4】________atoms. The output of light and heat of the Sun requires that some 600million tons of hydrogen are converted into helium in the Sun every【S5】________second. This the Sun has been done for several thousands of millions of【S6】________years. The nuclear energy is released at the Sun’s center as high-energy gamma radiation, a form of electromagnetic radiation like light and radiowaves, only of very much short wavelength. This gamma radiation is【S7】________absorbed by atoms inside the Sun, to be reemitted at slight longer【S8】________wavelengths. This radiation, in its turn, is absorbed and remitted. As the energy filters through the layers of the solar interior, it passes through the X-ray part of the spectrum, eventually becoming light. Atthis stage, it has reached that we call the solar surface, and can escape【S9】________into space, without being absorbed further by solar atoms. A very smallfraction of the Sun’s light and heat emitted in such directions that, after【S10】________passing unhindered through interplanetary space, it hits the Earth.《问题》：【S7】