完成式不定词
完成式不定词多数会出现在第三类条件句，用作完成条件式的一部分；但完成式不定词也可用在其他句型上。完成不定词的构成为：
to have + 过去分词
如同现在式不定词，有些时候必须用上不带 to 的被动语态不定词，因此 to 会被省略掉。这种情况会发生在多数情态助动词后，以及用在其他使用零不定词的地方。
举例
- He pretended to have seen the film.
- Before I turn 40, I want to have written a book.
- I would like to have been to the Taj Mahal when I was in India.
- If I had known you were coming I would have baked a cake.
- Someone must have broken the window and climbed in.
- That man may have noticed the bank robbers' getaway car.
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