So far I've leaned 3 different ways to ask "why?" in Icelandic: af hverju, hvers vegna, hví. Is there any difference between these words, or are they completely interchangeable? What is the difference, if any? For example, if I wanted to say this simple sentence in Icelandic, could I use all three words interchangeably? "Why did you move to Sweden?" Af hverju fluttir þú til Svíþjóðar? Hvers vegna fluttir þú til Svíþjóðar? Hví fluttir þú til Svíþjóðar?