托福几大常考话题背景知识，ets再骄傲放纵也不害怕！
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近几次托福考试写作部分都是之前考过的题目，托福考试重复14/15年老题的时候也很多。但是并没有什么卵用，该写跑偏还是要跑偏，之前听不懂读不懂的就算做了一遍也常常依旧不懂不懂。
死磕每篇题目肯定是不行的，要是考试赶上出新题呢？根本上解决当然是背单词和苦练整体的阅读、听力技能。但是有宝宝表示，苦练了啊，其他的都做的挺好可一碰见生物/地质/xx就凉了有木有？！碰上这种问题，首先我们要善用伟大的tpo，找出这个话题主题的那些篇题目，一起做。背那些影响你理解的生词。其次，就是稍微了解点背景知识，给自己个信心。
当然了，也不能迷信背景知识，虽然托福考试在阅读和听力部分会涉及一些专业学科，学科，话题涵盖了社会科学、人文科学以及 hard science等，听起来十分可怕。然而，ets 命题人表示：这些内容虽然涉及学科宽泛，考生可能并没有相关学科经验，但是涉及的内容只是基本的理论和概念——对于理解背景知识相当基础、相当宽泛的内容。
所以说，其实背景知识并不是必要的，只要词汇扩充到、能力提升上去，通过tpo了解点也就够了。看背景知识的意义在于，给你添加信心，顺带在备考期，让我们投入文章更顺利，进入状态更快速。
从整体的大话题来说，像是阅读，生物、历史、地质类是常考的阅读文章类型。艺术、生物、天文、地理、生态、历史、考古是听力常考的类型。细分下来阅读的生物类关于动物的话题出现的比较多，考察动物行为、动物特征、物种的变化等。历史类文章的考察频度紧随其后，不仅出现美国历史的相关材料，还纳入了欧洲历史、中东历史，甚至还有亚洲历史。其中考得多的一些话题是：城市化的发展、工业革命、玛雅文明、古罗马文明和道路交通的发展。就比如说1月6日和13日的考试都考察了工业革命。地质类的文章多考察地球地质状况的变迁及带来的影响。比如板块构造学说、大陆漂移学、冰川变化等等。
近期考到的例子
工业革命
在历史相关的文章和学术讲座中，18 世纪发生在英格兰中部地区的工业革命是非常常见的事件，这场工业革命影响了整个欧洲大陆，并带动当时许多国·家相继发生工业革命。工业革命的发展特点、历史甚至与之相关的蒸汽机、能源问题都是在阅读和听力中经常出现的话题。
tpo 26 中就曾出现蒸汽机以及蒸汽机改良相关的细节描述：
in the late 1700s james watt designed an efficient and commercially viable steam engine（蒸汽机） that was soon applied to a variety of industrial uses as it became cheaper to use....a rotary（转动的，旋转的） engine attached to the steam engine enabled shafts（转动轴） to be turned and machines to be driven, resulting in mills using steam power to spin and weave cotton.
同一篇中，谈到工业革命中钢铁行业的发展，也具体到很多细节：
the availability of steam power and the demands for new machines facilitated the transformation of the iron industry.charcoal（木炭）, made from wood and thus in limited supply, was replaced with coal-derived coke （焦炭）(substance left after coal is heated) as steam-driven bellows（风箱） came into use for producing of raw iron. impurities were burnt away with the use of coke, producing a high-quality refined iron（精铁）. reduced cost was also instrumental in developing steam-powered rolling mills capable of producing finished iron（高纯度的铁） of various shapes and sizes.
工业革命主要产业及背景总结：
纺织产业：
纺织机的演化：飞梭(flying shuttle) → 杼箱 → 珍妮纺纱机(spinning jenny) → 骡机 (spinning mule)→ 水力织布机 → 蒸汽动力驱动
运输行业革新：
1776 年煤矿中使用铁轨；
1814 年运煤的蒸汽机车问世；
1825 年世界上第一条铁路；
1844年，英国铁路长达 2235 英里；
钢铁行业革新：
1709 年，焦炭取代木炭炼铁；
1750 年，坩埚炼钢工艺，欧洲历史上钢一次被熔化冶炼。
寒武纪cambrian
寒武纪时期，大约50个门的大量多细胞生物（包括几乎所有现生生物的祖先）快速出现，称为“寒武纪生命大爆发”。寒武纪的生物形态奇特，和地球上的现生生物极不相同。
寒武纪生命大爆发起源—埃迪卡拉动物群
埃迪卡拉（ediacaran）动物群是1947年在澳大利亚中南部ediacara地区的庞德砂岩层中首先发现的，被认为是20 世纪古生物学相当重大的发现之一。
埃迪卡拉动物群包含多种形态奇特的动物化石：身体巨大而扁平、多呈椭圆形或条带形，具有平滑的有机质膜，是人们迄今为止发现的相当古老、相当原始的化石，也是在太古代地层中发现的相当有说服力的生物证据。
尽管有关埃迪卡拉型动物群的性质还有许多争议，但其奇怪的形态令许多学者相信，埃迪卡拉型动物群是后生动物出现后的第一次适应辐射，它们代表了后生动物出现以后的第一次辐射演化因此，可以认为埃迪卡拉型动物群是在元古宙末期大气氧含量较低的条件下后生动物大规模占领浅海的一次尝试，结果失败了，而导致绝灭。在后来的演化过程中，后生动物采取了第二种方式，使内部的器官复杂化和物种多样化的发展，即生物系统演化。
去年11月26日考过的，2015年9月5日的原题寒武纪大爆发真题还原：
the cambrian explosion
the earliest fossil evidence for eukaryotes complex organisms whose cellscontain a distinct nucleus dates to only about 1.2 billion years ago. thefossil record suggests that animal evolution progressed slowly, with relativelylittle change seen between fossils from 1.2 billion years ago and those from ahalf-billion years later. but then something quite dramatic happened as can bejudged by the many different animal groups that suddenly appear in the fossilrecord.
biologists classify animals according to their basic body plans. for example,the basic body plan shared by mammals and reptiles is fundamentally differentfrom that of insects. animals are grouped by body plan into what biologistscall phyla. mammals and reptiles both belong to the single phylum chordata,which includes animals with internal skeletons. insects, crabs, and spidersbelong to the phylum arthropoda, which contains animals with body features suchas jointed legs, an external skeleton, and segmented bodies. classifyinganimals into phyla is an ongoing project for biologists, but modern animals appear to comprise about 30different phyla, each representing a different body plan.
remarkably, nearly all of these different body plans, plus a few othersthat have gone extinct, make their first known appearance in the geologicalrecord during a period spanning only about 40 million years, less than about 1percent of earth"s history. this remarkable flowering of animal diversityappears to have begun about 545 million years ago, which corresponds to the start of the cambrianperiod. hence it is called the cambrian explosion.
the fact that the cambrian explosion marks the only major diversificationof body plans in the geological record presents us with two important andrelated questions: why, so long after the origin of eukaryotes, did the pace ofevolution suddenly accelerate dramatically at the beginning of the cambrian,and why hasn"t there been another period of similarly explosive diversificationsince then ?
we can identify at least four factors that might have contributed to thecambrian explosion. first, the oxygen level in our atmosphere may have remainedwell below its present level until about the time of the cambrian explosion.thus, the rapid diversification in animal life may have occurred at least in partbecause oxygen reached a critical level for the survival of larger and moreenergy-intensive life forms.
a second factor that may have been important was the evolution of genetic complexity. as eukaryotes evolved, theydeveloped more and more genetic variation in their dna. some scientists believethat the cambrian explosion marks the point at which organisms developedcertain kinds of genes (homeobox genes) that control body form and that couldbe combined in different ways, allowing the evolution of a great diversity of forms over time.
a third factor may have been climate change. geological evidence pointsto a series of episodes in which earth froze over before the cambrian began.the extreme climate conditions of these episodes eliminated many species,leaving a wide array of ecological niches available into which new speciescould rapidly evolve when climate conditions eased at the beginning of thecambrian.
a fourth factor may have been the absence of efficient predators. early predatory animals were probably not verysophisticated, so some evolving animals that later might have been eliminatedby predation were given a chance to survive, making the beginning of thecambrian period a window of opportunity for many different adaptations toestablish themselves in the environment.
this last idea may partly explain why no similar explosion of diversityhas taken place since the cambrian: once predators were efficient andwidespread, it may have been virtually impossible for animals with entirely newbody forms to find an environmental niche in which they could escape predation.or it may be that while more body plans may have been possible at some earlypoint in evolution, it was not possible to evolve into those other body plansfrom the body plans that evolved in the cambrian. or perhaps the various bodyforms that arose during the cambrian explosion represent the full range offorms possible given the basic genetic resources that characterize all earth"sorganisms. in any case, no fundamentally new body forms have emerged sincethe cambrian explosion.
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