問題詳情

Questions 23~32The most easily recognizable meteorites are the iron variety, although they only represent about 5 percent of all meteorite falls. They are composed of iron and nickel along with sulfur, carbon, and traces of other elements. Their composition is thought to he similar to that of Earth's iron core3 and indeed they might have once made up the core of a large planetoid that disintegrated long ago. Due to their dense structure, iron meteorites have the best chance of surviving an impact, and most are found by farmers plowing their fields.One of the best hunting grounds for meteorites is on the glaciers of Antarctica1 where the dark stones stand out in stark contrast to the white snow and ice. Whenmeteorites fall on the continent) they are embedded in the moving ice sheets. At places where the glaciers move upward against mountain ranges, meteorites are left exposed on the surface. Some of the meteorites that have landed in Antarctica are believed to have conic from the Moon and even as far away as Mars, when large impacts blasted out chunks of material and hurled them toward Earth.Perhaps the world's largest source of meteorites is the Nullarbor Plain, an area of limestone that stretches for 400 miles along the southern coast of Western and South Australia. The pale, smooth desert plain provides a perfect backdrop for spotting meteorites, which are usually dark brown of black. Since very little erosion takes place, the meteorites are well preserved and are found just where they landed. Over 1,000. fragments from 150 meteorites that fell during the last 20,000 years have been recovered. One large iron meteorite, called the Mundrabilla meteorite, weighed more than 11 tons.Stony meteorites, called chordates, are the most common type and make up more than 90 percent of all falls . But because they are similar to Earth materials and therefore erode easily, they are often difficult to find. Among the most ancient bodies in the solar system are the carbonaceous chondrites that also contain carbon compounds that might have been the precursors of life on Earth.
23. What is the passage mainly about?
(A) Finding meteorites on Earth's surface
(B)How the composition of meteorites is similar to that of Earth
(C)Why most meteorites do not survive impact with Earth
(D)The origins of meteorites

參考答案

答案：A
難度：適中0.5
統計：A(3),B(0),C(1),D(2),E(0)

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