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。
How long have you been staying in America?
I want to know where she has gone.
How to solve the problem gives him a bad headache.
（How to solve the problem作主词。）
I don't know how to answer the question.
（how to answer the question作受词。）
The patient is in urgent need the medicine, but the problem is where to get it.
（where to get it作主词补语。）
When we are to start the competition hasn't fixed yet.
（When we are to start the competition作主词。）
She asked her husband where he had been.
（where he had been 作受词。）
The question is when we can finish our work.
（when we can finish our work作主词补语。）