结构推理 Directions: In this part there is a short passage with five questions or incomplete statements. Read the passage carefully. Then answer the questions or complete the statements in the fewest possible words (not exceeding 10 words). 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 converted into helium in the sun every second. The sun has been doing this for thousands of millions of years. 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 remitted at slightly longer 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 (光谱), 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 unhinderedly (不被阻碍的) through interplanetary space, it hits the earth. 1.What is the passage mainly about? 2.When is energy in the sun released? 3.According to the passage, we know that gamma waves 4.Through what does the energy released in the sun pass before it becomes light according to the passage? 5.From this passage we can draw a conclusion that the sun's light travels