who what which when where how后加不定式在句中可以做主语、宾语、表语等,但why后加动词原型,是特例:
1.主语
e.g.When to start has not been decided.
何时动身还未决定.
2.宾语
e.g.He did not know whether to go there or not.
他不知该不该去那.
3.表语
e.g.The difficulty was how to cross the river.
困难在于怎样过河.
e.g.The question was where to go.
问题是去哪里?
4.双重宾语
e.g.I can tell you where to get this book.
我能告诉你从哪搞到这本书.
e.g.I asked him how to learn English.
我告诉他怎样学好英语.
5.有时疑问词前可用介词
e.g.I have no idea of how to do it.