The sun today is a yellow dwarf star.
It is {{U}}fueled{{/U}} by thermonuclear reactions near its center that convert
hydrogen to helium. The sun has existed in its present state for about 4
billion, 600 million years and is thousands of times larger than the
Earth. By studying other stars, astronomers can predict what the rest of the sun’s life will be like. About 5 billion years from now, the core of the sun will shrink and become hotter. The surface temperature will fail. The higher temperature of the center will increase the rate of thermonuclear reactions. The outer regions of the sun will expand approximately 35 million miles, about the distance to mercury, which is the closest planet to the sun. The sun will then be a red giant star. Temperatures on the earth will become too hot for life to exist. Once the sun has used up its t A. To alert people to the dangers posed by the sun. B. To discuss conditions on earth in the far future. C. To present a theory about red giant stars. D. To describe changes that the sun will go through. 更多"The sun today is a yellow dwarf sta"的相关试题: [单项选择]
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