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Starting in the mid-1990s, major American cities began a radical transformation. Years of high violent crime rates, thefts, robberies, and inner-city decay suddenly started to turn around. Crime rates didn't just hold steadily, and they began falling faster than they went up.(1)____ That trend appeared in practically every post-industrial American city, simultaneously.(2)____
"The drop of come in the 1990s effected all geographic areas and demographic groups," Steven D. Levitt wrote in his landmark paper on the subject, Understanding Why Crime Fell in the 199Ds, and elucidated further in a best-selling book Freakonomics.(3)____(4)____ "It was unanticipated that it was widely dismissed as temporary or illusory long after it had begun.(5)____" He went on to tie the drop to the legalization of abortion 20 years much earlier, dismissing police tactics as a cause but they failed to explain the universality and unexpectedness of the change.(6)____(7)____ Alfred Blumstein's The Crime Drop in America pinned the cause of crime solely on the crack epidemic but gave the credit for its appearance to those self-same policing strategies.(8)____
Plenty of other theories have been offered to account for the double-digit decrease in violence, from the advent of "broken windows" policies, three strikes laws, changing demographics, gun control laws, and the increasing prevalence of cellphones or an upturn in the economy and cultural shifts in American society. Some of these theories have disproven outright while othersrequire a healthy dose of assumption to turn correlation into causation.

答案解析
文章大意
本文讨论的是美国城市犯罪率的下降。20世纪90年代中期开始，美国城市犯罪率发生了根本的变化，以前居高不下的暴力犯罪、偷盗、抢劫等突然间开始好转，而且几乎同时发生在每个后工业时代的城市里。关于犯罪率下降的原因，大家各持己见，Steven D. Levitt把其归功于堕胎的合法化，而Alfred Blumstein则认为是警方策略，还有其他各种理论，包括各种政策法规的出现、手机的普及以及经济和文化等各方面，其中有些理论已经被彻底推翻，而另外一些还有待验证。
案案详解
1．steadily→steady语法错误。hold此处是“保持，持续”的意思，为系动词。其后应接形容词性的steady。
2．That→This语法错误。this和that都可以指代前面提到的事物，一般近指用this，表示“这个”，此处指代的就是前一句所提到的趋势，故应改为This。
3．effected—affected词汇错误。effect作动词意为“产生，引起”，affect作动词意为“影响”，根据上下文语义，此句要表达的意思是“90年代犯罪率的下降影响到了所有的地区和社群。”故应改为affected，符合上下文语境。
4．a→the词汇错误。此处用来特指Freakonomics这本书，故应改为the。
5．∧unanticipated→so语法错误。从结构上来看，这句话可以看成是that引导的主语从句，意思是“犯罪率下降被普遍认为是短暂的或虚幻的，这一观点是不曾预料到的”，但与上下文语境不符。此句中的it was widely dismissed as temporary or illusory应该是用来形容unanticipated的程度，故应该在前面增加一个so与that搭配，构成结果状语从句，意为“犯罪率下降是始料未及的，以致它被普遍认为是短暂的、虚幻的。”
6．much→much词汇错误。此处earlier作副词，表示“以前”，不需要much修饰。
7．but→because语篇错误。由上下文语义判断，句间的逻辑关系应该为因果关系，而不是转折关系，前句指出把犯罪率下降归功于20年前堕胎的合法化，不认为警方策略是导致下降的原因，后句说到警察手段不能解释犯罪率下降的普遍性及出乎意料性，后者指出前者的原因，故应该用表示原因的连词。
8．appearance→disappearance语篇错误。由上下文的语义判断，此处指酌是犯罪的消失而不是出现，故应改为disappearance。此句的意思是“Alfred Blumstein在《美国犯罪率下降》一文中把犯罪归咎于可卡因的泛滥，但把犯罪的消失归功于警察策略。”
9．or→to词汇错误。此处用to和前面的from搭配，构成from... to，列举了可能存在的other theories（其他理论）。
10.∧disproven→been语法错误。此句的主语Some of these theories与谓语动词disprove之间是被动关系，故应该加上一个been，表示现在完成时的被动语态。