The diference of niet and nee??
niet = not
nee = no
(geen = no / not a)
"Nee" is only used to give a negative answer to a yes/no-question. For the use of "niet" and "geen" see https://www.duolingo.com/comment/3734833
Does "nej" "neij" or however you'd want to spell that work as well?
No, it doesn't.
Why not geen?