it是省略：The box is too heavy for me to carry (it).

The box is ( ).

A. too heavy for me to carry

B. too heavy for me to carry it

书上说A当然正确，但是说B也是正确的。为什么呢？这是不定式的悬空结构吗？

麻烦老师详解一下，谢谢！

不定式悬空结构，仅限于这种类型：

The question is difficult to answer.

difficult to answer 应整体看作is 的表语。这时的不定式to answer 是表语的一部分。

如果difficult 之前加 too，那么不定式变成了结果状语。就可以说：

The question is too difficult to answer it.

The question is too difficult to be answered.

The question is too difficult for me to answer it.

The question is too difficult to be answered by me.

所以，The box is too heavy for me to carry it. 也正确。

刘永科 - 教育出版集团英语总顾问 & 英语系列图书主编

擅长：语法理论,语言学,文化背景 | 采纳率 86% | 回答于 1秒前

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曹荣禄 1秒前

擅长：动词用法,句法问题

too...to do结构中的悬空不定式是optional，即为选择性的，可以用悬空不定式，也可以用普通不定式。例如：

The book is too difficult for children to read (it).

另外，不定式作目的状语时，悬空不定式也是选择性的。例如：

I bought a new suitcase to put my clothes in (it).