请大家分析一下这三个从句是什么类型的从句?

请大家分析一下这三个从句是什么类型的从句?
括号里面的是从句.
1.There was a sudden flash, followed by (what sounds like that of the explosion of a bomb).
2.After (what seemed an endless wait), it was his turn to have the job interview.
3.You've no doubt heared people say how much they need a holiday, when (what they really mean is that they want one).