疑问副词：
用来引导特殊疑问句，表示时间，地点，方式，原因等。
常见的有：when,where,how,why等。
疑问副词的用法：
1.疑问副词是问何时、何地、如何、因何的副词，主要有when, where, how, why。
2.疑问副词用在句首。
How long have you been staying in America?
你在美国待多久了?
3.疑问副词在句中引导名词子句。
I want to know where she has gone.
我想知道她去哪里了。
4.疑问副词后接不定词构成的名词片语，在句中可以作主词、受词或主词补语。
How to solve the problem gives him a bad headache.
如何解决这个问题使他伤透脑筋。
（How to solve the problem作主词。）
I don't know how to answer the question.
我不知道如何回答这个问题。
（how to answer the question作受词。）
The patient is in urgent need the medicine, but the problem is where to get it.
这个病人急需这种药,但问题是哪里能找到。
（where to get it作主词补语。）
5.疑问副词引导的名词子句可作主词、受词或主词补语。
When we are to start the competition hasn't fixed yet.
我们什么时候开始比赛还没有定下来。
（When we are to start the competition作主词。）
She asked her husband where he had been.
她问她丈夫去哪里了。
（where he had been 作受词。）
The question is when we can finish our work.
问题是我们何时能完成我们的工作。
（when we can finish our work作主词补语。）
疑问代词与疑问副词的区别：
1. 疑问代词做对陈述句的主语，宾语或定语提问，即做句子的主语，宾语或定语，如what, who/ whom, whose.
eg. Who is talking ? What can you see?
Whose shirt is this?
2.疑问副词对时间，地点，方式等状语提问，如when, where, how 等.
eg. When is your birthday? Where are you going?
How do you know?
常见的疑问代词：what who which whom(只做宾语）
疑问副词：how where when
还有whether是疑问连接词。