How long do you think it would have been beforeyour lie was discovered?
这句话理解不好这个would have been，我能剖析出从句用了was discovered是表示谎话在说话时已经被揭穿了，但这里的would have been就让我的思维彻底乱套了，这到底是表示在目前推断过去谎话被揭穿之前，还是表示在过去推断过去谎话被揭穿之前，还是过去将完成时？感觉仿佛都对，但一定只有一个是对的不可以是都对呀.....跪求老师帮忙逐一剖析一下？谢谢老师！
How long do you think it would have been before your lie was discovered?
这句话，去掉目前时间的嵌入语 do you think，就是描述过去时间（过去以后）所发生状况的一个句子。
would have been 是针对过去以后状况的虚拟语气。虽然用 How long 询问，其实，是说明 “你的谎话被揭穿时间不会长了”。我演绎一下这个句子：
It will be a long time before your lie is discovered. （陈述语气，指向以后）
It would be a long time before your lie was discovered.（陈述语气，指向过去以后）
It would have been a long time before your lie was discovered.（主句虚拟语气，指向过去以后）