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。

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