<>的第一句:
At length I returned from two weeks leave of absence to find that my patrons had arrived three days ago in Roulettenberg
请问这个to 的从句是怎么引出来的呢？At length xxx to Or return from XXX to ?
At length
I returned from two weeks leave of absence这句话就是主句
to find that my patrons had arrived three days ago in Roulettenberg这是不定式作结果状语，一般用only to，往往表示意料之外或者不愉快的结果
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好像确实如果是only to 感觉句子就对了, thanks a lot 
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from A to B结构，A和B是并列成分，此句中from后是名词短语，to后是动词+that从句，故不是from … to …，而是to do不定式结构。进而可知是非谓语成分，找主干时可以直接划掉，就剩下 At length I returned from two weeks leave of absence. 如果知道return from短语，那句意就不难理解了。
你的回答是认真的吗(⊙x⊙;)二楼才是正解。
二楼才是正解！
seriously
I returned
I returned from leave of absence
I returned from two weeks leave of absence
I returned from two weeks leave of absence to find
I returned from two weeks leave of absence to find that my patrons had arrived three days ago in Roulettenberg
At length I returned from two weeks leave of absence to find that my patrons had arrived three days ago in Roulettenberg
不定式里嵌套了that从句
另外，有几个语言点值得学习：
at length, return from, leave of absence
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(only) to find 表达意料之外的结果吧
我猜是不定式引导的从句做伴随状语，省略掉这部分，剩下句子还是完整的。