Paragraph 3: The Allende meteorite is classified as a chondrite. Chondrites take their name from the Greek word chondros—meaning "seed"—an allusion to their appearance as rocks containing tiny seeds. These seeds are actually chondrules: millimeter-sized melted droplets of silicate material that were cooled into spheres of glass and crystal. A few chondrules contain grains that survived the melting event, so these enigmatic chondrules must have formed when compact masses of nebular dust were fused at high temperatures—approaching 1,700 degrees Celsius—and then cooled before these surviving grains could melt. Study of the textures of chondrules confirms that they cooled rather quickly, in times measured in minutes or hours, so the heating events that formed them must have been localized. It seems very unlikely that large portions of the nebula were heated to such extreme temperatures, and huge nebula areas could not possibly have lost heat so fast. Chondrules must have been melted in small pockets of the nebula that were able to lose heat rapidly. The origin of these peculiar glassy spheres remains an enigma.
4. The word "allusion" in the passage is closest in meaning to
O addition
O modification
O resemblance
O reference
词汇题
解析：Chondrites take their name from the Greek word chondros—meaning "seed"—an allusion to their appearance as rocks containing tiny seeds.通过同位语解释关系，可以知道，C陨石起名于希腊单词“种子”，因为他们石头的外形含有很多小种子；所以是一种指代，选4
5. The word "enigmatic" in the passage is closest in meaning to
O dangerous
O mysterious
O interesting
O surprising
词汇题
解析：A few chondrules contain grains that survived the melting event, so these enigmatic chondrules must have formed when compact masses of nebular dust were fused at high temperatures，根据上下文，只有很少的C陨石在这次事件中存活下来，所以存活下来的都是“奇迹”，应该是不同寻常的，神秘的，选2
6. According to paragraph 3, what does the presence of grains inside some of the chondrules indicate?
O The chondrules were formed of silicate material.
O The chondrules were formed at high temperatures and then cooled rapidly.
O The grains were formed in huge areas of the solar nebula
O The grains were formed after the chondrules were fused together into chondrites.
细节题
定位词：presence of grains inside some of the chondrules
解析：A few chondrules contain grains that survived the melting event, so these enigmatic chondrules must have formed when compact masses of nebular dust were fused at high temperatures—approaching 1,700 degrees Celsius—and then cooled before these surviving grains could melt.也就是C陨石在高温中形成并且很快的冷却，选2
Paragraph 4: Equally perplexing constituents of Allende are the refractory inclusions: irregular white masses that tend to be larger than chondrules. They are composed of minerals uncommon on Earth, all rich in calcium, aluminum, and titanium, the most refractory (resistant to melting) of the major elements in the nebula. The same minerals that occur in refractory inclusions are believed to be the earliest-formed substances to have condensed out of the solar nebula. However, studies of the textures of inclusions reveal that the order in which the minerals appeared in the inclusions varies from inclusion to inclusion, and often does not match the theoretical condensation sequence for those metals.
7. According to paragraph 4, all of the following are true about the minerals found in the refractory inclusions EXCEPT:
O These minerals are among the most resistant to melting of all the major elements in the solar nebula.
O These minerals are believed to be some of the first elements to have condensed out of the solar nebula.
O These minerals are among the least commonly found elements on Earth.
O These elements occur in the order that scientists would have predicted.
排除题
定位词: refractory inclusions
解析: However, studies of the textures of inclusions reveal that the order in which the minerals appeared in the inclusions varies from inclusion to inclusion, and often does not match the theoretical condensation sequence for those metals.也就是内含物的顺序和科学家所预期的不一样，原文正确的选项对应以下内容：Equally perplexing constituents of Allende are the refractory inclusions: irregular white masses that tend to be larger than chondrules. They are composed of minerals uncommon on Earth, all rich in calcium, aluminum, and titanium, the most refractory(resistant to melting) of the major elements in the nebula. The same minerals that occur in refractory inclusions are believed to be the earliest-formed substances to have condensed out of the solar nebula.选4
Paragraph 5: Chondrules and inclusions in Allende are held together by the chondrite matrix, a mixture of fine-grained, mostly silicate minerals that also includes grains of iron metal and iron sulfide. At one time it was thought that these matrix grains might be pristine nebular dust, the sort of stuff from which chondrules and inclusions were made. However, detailed studies of the chondrite matrix suggest that much of it, too, has been formed by condensation or melting in the nebula, although minute amounts of surviving interstellar dust are mixed with the processed materials.
8. The word "pristine" in the passage is closest in meaning to
O pure
O solid
O ordinary
O trapped
词汇题
解析：At one time it was thought that these matrix grains might be pristine nebular dust, the sort of stuff from which chondrules and inclusions were made.选1
9. According to paragraph 5, which of the following is indicated by studies of the mixture holding the inclusions together?
O Large amounts of this material were formed by condensation or melting in the nebula.
O This material contains more iron and iron sulfide than had previously been thought.
O This material is very similarto the material from which the refractory inclusions are made
O The grains in this material are made from the same elements as chondrules are.
细节题
定位词：studies of the mixture holding the inclusions together
解析：However, detailed studies of the chondrite matrix suggest that much of it, too, has been formed by condensation or melting in the nebula, although minute amounts of surviving interstellar dust are mixed with the processed materials.选1
Paragraph 6: All these diverse constituents are aggregated together to form chondritic meteorites, like Allende, that have chemical compositions much like that of the Sun. To compare the compositions of a meteorite and the Sun, it is necessary that we use ratios of elements rather than simply the abundances of atoms. After all, the Sun has many more atoms of any element, say iron, than does a meteorite specimen, but the ratios of iron to silicon in the two kinds of matter might be comparable. The compositional similarity is striking. The major difference is that Allende is depleted in the most volatile elements, like hydrogen, carbon, oxygen, nitrogen, and the noble gases, relative to the Sun. These are the elements that tend to form gases even at very low temperatures. We might think of chondrites as samples of distilled Sun, a sort of solar sludge from which only gases have been removed. Since practically all the solar system's mass resides in the Sun, this similarity in chemistry means that chondrites have average solar system composition, except for the most volatile elements; they are truly lumps of nebular matter, probably similar in composition to the matter from which planets were assembled.
10. In paragraph 6, why does the author mention that "the Sun has many more atoms of any element, say iron, than does a meteorite specimen"?
O To show how difficult it is to compare the composition of a meteorite with that of the Sun
O To explain why a comparison of the compositions of a meteorite and of the Sun has to be done in terms of ratios of elements
O To identify the most common element in both the Sun and meteorite specimens
O To emphasize how much largerthe Sun is than any meteorite specimen is
修饰目的题
定位词：the Sun has many more atoms of any element, say iron, than does a meteorite specimen
解 析：To compare the compositions of a meteorite and the Sun, it is necessary that we use ratios of elements rather than simply the abundances of atoms.答案在前一句话，提出黑体字的目的是为了为什么要比较陨石和太阳的成分。选2
