动词不定式的很有趣的用法。 它可以和特殊疑问词连用
如：
We can use a question word with a to-infinitive after a verb.
I don't know what to do now.
特殊疑问词+ to do/be 的用法：
1. 作宾语
有些及物动词的后面可以直接放上特殊疑问词+ 不定式来做宾语。
比如：
know what to do
ask when to leave
find where to ask for help
例句：
（1）Daniel did not say who to talk to about this book?
（2）Kitty cannot decide which to choose first.
（3）Sandy is wondering where to ask for help.
（4）Amy does not know how to write the report.
2. 作宾语补足语
可以跟在一个宾语后面来补充说明这个宾语一些情况， 这种成分成为宾语补足语，简称宾补。
例：
（1）Mr Wu advised us which to choose as after-school activities.
（2）The students asked their teacher when to hand in their work.
（3）Millie showed us what to do next.
（4）Daniel taught himself how to use a computer to draw.
疑问句的四种疑问方式分别为一般疑问句、特殊疑问句、反义疑问句和选择疑问句。
一般疑问句的例子：你是不是要去上课了？解释一般疑问句是疑问句的基本形式，语调应该上扬。
特殊疑问句的例子：你在哪里上学？解释特殊疑问句是询问某一特定信息的疑问句。
反义疑问句的例子：你是不是不喜欢吃蔬菜？解释反义疑问句是用相反的意思来表达询问，通常用于确认对方的意见或观点。
选择疑问句的例子：你喜欢吃汉堡还是炸鸡？解释选择疑问句是用于询问两个或多个选项之一的疑问句。
当由疑问代词引导的宾语从句,从句的主语与主句的主语一致时改为简单句，或者疑问代词作实义及物动词的宾语时，可以用疑问代词+动词不定式结构。即：
what to do.
who to do.
which to do.
……
例句：
1.Please tell me what I should do next.改为简单句是：
Please tell me what to do next.
2.I wonder who I should ask.