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第十八单元 推展段落方法之九因果法（Ⅱ） 18.1原因法 有时，一个结果会源于几个原因。同样，段落可或以结果开头或以结果结束，作者可以从熟悉到不熟悉的原因逐一分析，或是从分析一个又一个读者不熟悉的原因开头，最后引出读者熟悉的结果。选用哪一种，决定于作者认为哪一种更有说服力。 示范段落18-1 Several changes have brought wild animals to the cities.Foremost is，that air and water quality in many cities have improved as a result of the 1970s pollution control efforts.Meanwhile，rural areas have been built up，leaving many animals on the edges of suburbs.In addition，urban wildlife refuges have been created.The Greater London Council last year spent ＄750，000 to buy land and build 10 permanent wildlife refuges in the city.As a result，many big birds are now living in the city.For peregrine falcons cities are actully safer than rural cliff dwellings.By 1970 the birds had died out east of the Mississippi because DDT had made their eggs too thin to support life.That year，scientist Tom Cade of Cornell University began raising the birds for release in cities，for cities afforded plentyof food. 18.2 示范段落分析 主题句：Several changes have brought wild animals to the cities. 因果模式（Cause-effect Pattern）： | 
