一、英语语法 —— 疑问词+不定式

基本用法说明

疑问代词 who, whom, what, which, whose; 疑问副词 when, how, where 与不定式结合可形成短语，用于句中的主语、宾语或表语。

1. 作主语：

   • What to do is not decided yet. (该做什么还没有决定)
   • How to begin is more difficult than where to stop. (如何开始比如何停止更难)

2. 作宾语： （常接在 forget, find out, discuss, decide, tell, teach, know, learn, wonder, remember 等动词之后）

   • Do you know when to start? (你知道什么时候开始吗？)
   • She showed her which button to press. (她告诉她按哪个按钮)

3. 作表语：

   • The question is how to carry out the plan. (问题是如何执行这个计划)
   • The difficulty was how to cross the river. (困难在于如何过河)

疑问词还可以用于特定动词（know, imagine, learn, decide, forget, remember, consider, understand）后的不定式短语：

• He didn’t know how to answer her. (他不知道怎么回答她)
• I don’t know who to ask advice from. (我不知道向谁请教)
• Please explain (to me) where to begin and how to do it. (请向我解释从哪里开始以及怎么做)

3. 作名词同位语：

   • Tom had no idea which book to read first.
   • The question whether to confess troubled the girl.

4. 用于直接宾语。某些动词后可接 “sb.+ 疑问词 + 不定式” 构成的双重宾语，这类动词常用的有 advise, ask, show, teach, tell 等如：

   • I can tell you where to get this book.
   • I ask her how to learn English.
   • He will advise you what to do.
   • Will you show me how to use the machine?

5. 作介词宾语： 某些介词后面可接 “疑问词＋不定式” 作宾语，这类介词常用的有 about, as, from, in, of, on, with 等。例如：

   • He has no idea of how to answer this question. 他不知道怎样回答这个问题。
   • Della had only $1.87 with which to buy Jim a present. 德拉仅有$1.87为来吉姆买一件礼物。(which是关系代词)
   • You have a number of topics from which to choose. 你有很多题目可以选择。(which是关系代词)

二 “特殊疑问词＋动词不定式” 这种结构可以把复合句转为简单句

• I don’t know what I’ll do next. = I don’t know what to do next. 我不知道接下来该做什么。
• The doctor told him when he should take the medicine. = The doctor told him when to take the medicine. 医生告诉他应该什么时候服药。

同样，因为 “特殊疑问词＋动词不定式” 这种结构相当于一个名词性从句，所以可用同等成分的从句代替，从而把简单句转换为复合句。改写时只需在疑问词后加上适当的主语，并把不定式改为适当的形式的谓语即可。如：

• Which to choose is important. = Which we should choose is important. 我们应该选择哪个是重要的。
• The question is where to go. = The question is where we should go. 问题是我们应该去哪里。

三、“特殊疑问词＋动词不定式”这种结构可构成独立问句。如：What to do? 怎么办？How to get rid of the trouble? 如何摆脱困境？

四、注意

五个易错点

1. 易错点一： why 之后使用不定式
   • 疑问副词why 后不直接跟动词不定式，如：
     • 误：I don’t know why to choose that dictionary.
     • 正：I don’t know why you must choose that dictionary. 我不知道为什么你必须选择那本字典。
   • 但它可以接不带 to 的动词不定式，即动词原形，构成 why do sth./ why not do sth. 肯定形式是表示某动作是不必要的或没有意义的，而否定形式是表示向某人提建议和表达看法，相当于祈使句。
     • Today is Sunday. Why not go out to relax yourself? 今天是星期天。为什么不出去放松一下呢？
     • Why pay more at other shops? We have the best value 为什么在其他商店支付更多？我们提供最优惠的价格。
2. 易错点二： 与动词 think 连用
   • 当“疑问词+不定式”与动词think连用时，通常用于think的现在或过去式之后。
   • She couldn’t think what to say. (她想不出该说什么)
3. 易错点三： 与动词know连用
   • 当某些疑问词“疑问词+不定式”与动词know连用时，know之后的宾语从句需改为不定式结构。
   • I know how to make Spanish omelettes. (我会做西班牙煎蛋卷)
4. 易错点四： “疑问词+不定式”与动词解释
   • 通常用于直接解释如何做某事的情况下。
   • Can you explain how to make a cake? (你能解释如何做蛋糕吗？)
5. 易错点五： 疑问词 to do 间或有时可由从句替换
   • 当使用“疑问词+不定式”时，有时可以替换为相应的从句。
   • Did you ask her which to buy? (你问她买哪个了吗？)

References

“特殊疑问词＋动词不定式”的用法归纳

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