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华慧考博-考博英语两个复杂句子的结构分析(三十一)
1. Unchallenged by such infections for so long, people have little immunity to waterborne pathogens and so are at greater risk of contracting diseases when the system breaks down.
【结构分析】句子主干为：people have little immunity to waterborne pathogens and so are at greater risk of contracting diseases；“when the system breaks down”为when引导的时间状语从句；“Unchallenged by such infections for so long”相当于分词短语充当状语表示原因。
2. Even among the 50 percent of smokers who said they had not changed their habits, the test showed that about half had in fact cut down.
【结构分析】句子主干为：the test showed that about half had in fact cut down，这里that引导其后的部分充当showed的宾语；“among the 50 percent of smokers”为地点状语；“who said they had not changed their habits”为who引导的从句充当“smokers”的后置定语。
