单选题 The sun today is a yellow dwarf star. It is fueled 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 thermonuclear energy as a red giant, it will begin to shrink. After it shrinks to the size of the earth, it will become a white dwarf star. The sun may throw off huge amounts of gases in violent eruptions called nova explosions as it changes from a red giant to a white dwarf.
After billions of years as a white dwarf, the Sun will have used up all its fuel and will have lost its heat. Such a star is called a black dwarf. After the Sun has become a black dwarf, the earth will be dark and cold. If any atmosphere remains there , it will have frozen onto the earth"s surface.
单选题 What is the primary purpose of this passage?
【正确答案】 D
【答案解析】[解析] 主旨题型
本文主要谈论了：如今的太阳是个黄色的矮星，由靠近它中心的高热原子核反应将氢转化为氦来提供燃料。……天文学家通过研究其它星球，能够预测太阳的余生/未来会是什么样子。距今大约五十亿年后，太阳的核会缩小并且会变得更热，而太阳表面的温度会降低……然后太阳将会成为一个红色的巨星。地球上的温度会变得过热，以至没有生命能够存活。
一旦太阳耗尽了红色巨星的高热原子核反应的能量，它会开始缩小；等它缩小到地球的大小时，它将会变成个白色的矮星；当它从一个红色巨星变成一个白色矮星时，太阳会以剧烈喷发的形式释放大量的被称之为“新星爆发”的气体。在变成白色矮星的几十亿年后，太阳会耗尽它所有的燃料，热度消失；这样的一个星被称之为黑色矮星……由此得知本文的主要目的是谈论太阳所要经历的变化，因此D为答案。
单选题 The word "fueled" underlined in Paragraph 1 most probably means ______ .
【正确答案】 A
【答案解析】[解析] 词义题型
A．powered产生动力；B．bombarded炮轰，轰击；C．created创造；D．pushed推动；参照注释51。太阳由靠近它中心的高热原子核反应将氢转化为氦来……因此A为答案。
单选题 It can be inferred from the passage that the sun ______ .
【正确答案】 A
【答案解析】[解析] 推断题型
从文章第二段第一句得知，天文学家通过研究其它星球，能够预测太阳的余生/未来会是什么样子。文章没有谈及太阳已存在了多少年，选项B不对；尽管文章谈了太阳所要经历的变化，但这一过程是极其缓慢的，选项C也不对；文章第二段提到：距今大约五十亿年后，太阳的核会缩小并且会变得更热，而太阳表面的温度会降低，然后太阳将会成为一个红色的巨星，因此选项D也不对；所以A为答案。
单选题 What will probably be the first stage of change as the sun becomes a red giant?
【正确答案】 D
【答案解析】[解析] 细节题型
见第二段第二句并参照注释51：距今大约五十亿年后，太阳的核会缩小并且会变得更热，而太阳表面的温度会降低，然后太阳将会成为一个红色的巨星；因此D为答案。
单选题 When the sun becomes a red giant, what will conditions be like on Earth?
【正确答案】 C
【答案解析】[解析] 细节题型
见第二段最后一句Temperatures on the Earth will become too hot for life to exist．(地球上的温度会变得过热，以至没有生命能够存活。)C为答案。
单选题 As a white dwarf, the sun will be ______ .
【正确答案】 B
【答案解析】[解析] 细节题型
见第三段第一、二句：一旦太阳用尽了它作为一个红色巨星的热核能，它就开始缩小；等它缩小到地球的大小时就会变成一个白色的矮星。所以B为答案。
单选题 According to the passage, which of the following best describes the sequence of stages that the sun will probably pass through?
【正确答案】 C
【答案解析】[解析] 是非题型
通读全文，可得出结论：太阳的演变过程是Yellow dwarf，red giant，white dwarf；black dwarf，所以C为答案。
单选题 The phrase "throw off" underlined in Paragraph 3 most probably means ______ .
【正确答案】 A
【答案解析】[解析] 词义题型
见第三段最后一句：当太阳从一个红色巨星变成一个白矮星时，它会以猛烈喷发的形式 ______ 大量的气体，这被称之为新星爆发。而A．eject逐出，喷射；B．bum up烧掉，发怒；C．convert使转
变；D．let in放进，允许……进入；因此A为答案。
单选题 The word "there" underlined in Paragraph 4 refers to ______ .
【正确答案】 A
【答案解析】[解析] 词义题型
见最后一段最后两句：最后一句中的there指的是上一句的主语the Earth，因此答案为A。
单选题 Which of the following best describes the tone of the passage?
【正确答案】 D
【答案解析】[解析] 态度题型
作者在叙述本文时直截了当，也没掺杂个人的情感，就事论事；因此答案为D。