In July of 1994, an astounding series of events took place. The world anxiously watched as, every few hours, a hurtling chunk of comet plunged into the atmosphere of Jupiter. All of the twenty-odd fragments, collectively called comet Shoemaker-Levy 9 Line after its discoverers, were once part of the same object, now dismembered and strung out (5) along the same orbit. This cometary train, glistening like a string of pearls, had been first glimpsed only a few months before its fateful impact with Jupiter, and rather quickly scientists had predicted that the fragments were on a collision course with the giant planet. The impact caused an explosion clearly visible from Earth, a bright flaming fire that quickly expanded as each icy mass incinerated itself. When each fragment slammed (10) at 60 kilometers per second into the dense atmosphere, its immense kinetic energy was transformed into heat, producing a superheated fireball that was ejected back through the tunnel the fragment had made a few seconds earlier. The residues form these explo-sions left huge black marks on the face of Jupiter, some of which have stretched out to from dark ribbons. (15) Although this impact event was of considerable scientific importance, it especially piqued public curiosity and interest. Photographs of each collision made the evening television newscast and were posted on the Internet. This was possibly the most open scientific endeavor in history. The face of the largest planet in the solar system was changed before our very eyes. And for the very first time, most of humanity came to fully appreciate the (20) fact that we ourselves live on a similar target, a world subject to catstrophe by random assaults from celestial bodies. That realization was a surprise to many, but it should not have been. One of the great truths revealed by the last few decades of planetary explo-ration is that collisions between bodies of all sizes are relatively commonplace, at least in geologic terms, and were even more frequent in the early solar system. 3. The author compares the fragments of comet Shoemaker-Levy 9 to all of the following EXCEPT (A) a dismembered body (B) a train (C) a pearl necklace (D) a giant planet 答案：D By far the most important United States export product in the eighteenth and nineteenth centuries was cotton, favored by the European textile industry over flax or wool because it was easy to process and soft to tile touch. Mechanization of spinning and Line weaving allowed significant centralization and expansion in the textile industry during (5) this period, and at the same time the demand for cotton increased dramatically. American producers were able to meet this demand largely because of tile invention of the cotton gin by Eli Whitney in 1793. Cotton could be grown throughout the South, but separating the fiber—or lint—from the seed was a laborious process. Sea island cotton was relatively easy to process by hand, because its fibers were long and seeds were (10) concentrated at the base of the flower, but it demanded a long growing season, available only along the nation’s eastern seacoast. Short-staple cotton required a much shorter growing season, but the shortness of the fibers and their mixture with seeds meant that a worker could hand-process only about one pound per day. Whitney’s gin was a hand-powered machine with revolving drums and metal teeth to pull cotton fibers away from (15) seeds. Using the gin, a worker could produce up to 50 pounds of lint a day. The later development of larger gins, powered by horses, water, or steam, multiplied productivity