英语有个很有用的结构，就是：疑问词+不定式动词(question word + to-infinitive)。

疑问词是疑问代词“who, whom, what, which, whose”和疑问副词“when, where, how, why ”。此外，连接词“whether”也适用。

“疑问词+不定式动词”结构有何功用呢?其主要功用有下列五种：

⑴当主语，如：

● When to hold the meeting has not yet been decided.

● Where to live is a problem.

● How to cope with the rising cost of living becomes a daily discussion topic.

⑵当宾语，如：

● We must know what to say at a meeting.

● He could not tell whom to trust.

● Do you know how to play bridge?

⑶当补足语，如：

● The problem is where to find the financial aid.

● The question is who to elect.

⑷当名词同位语，如：

● Tom had no idea which book to read first.

● Do you have a rough impression how to do it?

⑸当宾语补足语，如：

● Jim is not sure whose to choose.

● Mary and John are not certain whether to get married or not.

适用于“疑问词+不定式动词”的动词包括：“know, see, decide, tell, ask, consider, discover, explain, forget, guess, hear, imagine, inquire, learn, remember, think, wonder, understand”等。

有点值得特别注意的是：当这结构当宾语时，它的作用等于名词分句，例如：

● I could not decide which dictonary to buy. / I could not decide which dictionary I should buy.

● Jack did not know where to find such a good teacher./ Jack did not know where he could find such a good teacher.

有些动词，如“ask, show, tell, advise, inform, teach”等，可以先有个宾语，然后才接着加上适当的“疑问词+不定式动词” 结构。例如：

● The chief technician showed the apprentice how to repair the machine.

● Have you told him where to get the application form?

综上所述，可见“疑问词+不定式动词”结构是个形象清新，既容易用又不容易出错的特别结构，可以多多运用。