Such is human nature, that a great many people are often willing to sacrifice higher pay for the privilege of becoming white-collar workers. [《新概念英语》(新版)(3), 外研社, p.26] 该书在课文注释(p.26)中说：“such 位于句首，起强调作用，后面要用倒装语序，that 引导的是 such 的同位语从句”。
您也认为 that 从句是 such 的同位语从句吗？
上句的正常语序是 Human nature is such that ...。这是一个很常见的句型,其中的 that 从句应分析为结果状语从句。例如：
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His reactions are such that no one can match him. 他反应之敏捷,没有人能比得上。
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The performance was such that the audience were deeply moved. 演出那么精彩,观众深受感动。
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The extent of the disaster was such that the local authorities were quite unable to cope with. 灾难达到如此严重的程度，以至于地方当局无法应付。
当 such 位于句首时,该句型的本质并未发生变化:
Such was his strength that he could bend irons. 他的力气大得能把铁棍弯过来。
拿你提问的句子来说,that 从句显然是个结果状语从句:人性竟是如此,以致于许多人……
说 that 从句是 such 的同位语从句恐怕缺乏根据。一是很难找到类似的实例，二是从语义上说 that 从句不可能是 such 的同位语: such ≠ a great many people are often willing to。
[附注]上面的 such that 和 such ... that 与 such a + 名词 + that 三种结构中的 that 从句都是结果状语从句：
Jimmy made such a noise that his sister told him to be quiet. 吉米弄出那么大的声音，以致他的姐姐告诉他安静些。
请做下面的英语试题：
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It's such an interesting story ____ everybody likes it. A. as B. that C. so that D. which
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____ was his diligence that everyone praised him. A. So B. Such C. It D. What
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____ was her bravery that they were all frightened. A. So B. This C. That D. Such
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There was such a long line at the exhibition ____ we had to wait for about half an hour. A. so B. as C. that D. hence(全国四级,02.1-41)
suffice it to say 见 God bless you