文档介绍：It作形式主语和形式宾语，虽然是我们高中就学过的语法点，但在考研英语题型中，无论是在阅读还是翻译，常会考查该知识点。
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英语中不定式、动名词、主语从句在作主语时主语往往显得很长，使整个句子看上去有点头重脚轻，ouring fumes into the air until we know for sure。(2005 Text2)
【结构分析】本句的主干是voices come from…，现在分词短语insisting…作voice的后置定语，insiste后接两个 that引导的宾语从句，分别为that the science about global warming is incomplete和that it’s OK to keep pouring fumes into the air until we know for sure，第二个that从句中，it是形式主语，真正的主语由不定式短语充当，until we know for sure为时间状语从句。
【参考译文】就像吸烟问题一样，来自不同领域的声音坚持认为有关全球气候变暖的科学资料还不完整。在我们证实这件事之前可以向大气中不断地排放气体。
主语从句做句子真正主语，其结构组成一般是“形式主语it +谓语+ 关系连词+从句”。
例句1：Further more，it is obvious that the strength of a country’s economy is directly bound up with the efficiency of its agriculture and industry, and that this in turn rests upon the efforts of scientists and technologists of all kinds. (2000-72)
【结构分析】本句主干为it is obvious that…，其中it是形式主语，真正的主语为and连接的两个that引导的名词性从句that the strength of a country’s economy is…和that this in turn rests…。第一个主语从句中，代词its指代 country’s;第二个主语从句中，this指代 efficiency of its agriculture and industry。
【参考译文】再者，显而易见的是一个国家的经济实力与其工业生产效率密切相关，而效率的提高又有赖于各种科技人员的努力。
例句2：It’s not obvious how the capacity to visualize objects and to figure out numerical patterns suits one to answer questions that have eluded some of the best poets and philosophers。(2007Text2)
【结构分析】本句中It为形式主语，真正主语是其后how引导的主语从句，how the capacity suits one to answer questions，两个