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長難句分析
Today the most famous selfreplicating molecule is DNA (deoxyribonucleic acid), but it is widely thought that DNA itself could not have been present at the origin of life because its replication is too dependent on support from specialized machinery, which could not have been available before evolution itself began.
該句是一個(gè)由but連接的并列句。前一個(gè)分句較簡單，主干為The most famous selfreplicating molecule is DNA... 。后一個(gè)分句結(jié)構(gòu)復(fù)雜，嵌套了多層從句，其主干是it is widely thought that...；it為形式主語，真主語是that引導(dǎo)的從句；because引導(dǎo)了一個(gè)較長的原因狀語從句，其中又嵌套了which...非限定性定語從句做 machinery 的后置定語；from... 介詞短語后置修飾support。
