【难句】The energy used to separate oxygen from air before burning is almost as great as that needed to filter out nitrogen afterwards, leading to a similar loss of efficiency. (The Economist Nov. 30, 2006)。

【结构分析】本句是一个简单句，为一个主系表结构The energy is almost as great as that needed to filter out nitrogen afterwards，使用了as…as…结构，其中被比较的对象that needed to filter out nitrogen afterwards中，that指代上文的energy，过去分词结构needed to…作后置定语体现被动。其中主语energy由过去分词结构used to separate oxygen from air before burning 作后置定语体现被动;句末的现在分词结构leading to a similar loss of efficiency作全句的结果状语。

【参考译文】 燃烧前将氧气从空气中分离所需的能源几乎不亚于上述将氮气过滤所需的耗费，这就使得两者在效率损失上不相上下。