hast du dich
= Which one did you decide to take?
188.8.131.52.2 Adjectival pronoun
Auto willst du nach Italien fahren?
= In which car would you like to go to Italy?
Tisch hast du die Schlüssel gelegt?
= On which table did you put the keys?
* Of course one could also ask: In what car would you
like to go to Italy? But this would mean in 'what kind
of car', which would be in German 'in was für einem
Auto willst du nach Italien fahren?'. And still then the
difference is quite subtle.