1、作主语
When to start remains undecided.何时出发,尚未决定.
Where to live is a problem.去哪里住是一个问题.
2、作宾语
I don't know what to do.我不知道怎么做.
She didn’t know which bus to take.她不知乘哪路公共汽车.
The teacher showed us how to read a book.老师指点我们怎样读书.
The dictionary didn’t tell the Frenchman how to pronounce the word .那本词典没有告诉那个法国人怎样读那个词.
3、作表语
The difficulty is how to do the most of work with the least of money.困难是如何尽量少用钱多办事.
The question is who to elect.问题是该选谁.
4、作补足语
Jim is not sure whose to choose.Jim不能确定选择什么.
Mary and John are not certain whether to get married or not.Mary和 John不能确定是否要结婚.