did you go to the beach <-> when did you go to the beach
Is he walking to school <-> where is he walking to?
Have they gone? <-> where have they gone?
wie - who: who did you meet at the pub?
wat - what: what did you do when you were in London?
wanneer- when: when does she go to school
waar - where: where have you been?
waarom - why: why is he talking to her? - why isn't he talking to her?
Welke - which: which countries haven't you been to?