If I put "which" instead of what is that wrong?
No. "What" is more common in such context....
Well, I think in this context there is a more open set of possibilities (differences in this case) so "what" is more appropriate; nevertheless "wich" is grammatically correct.
That what I meant. You're right. You can report the problem..
Ok, thank you ;)
"Which" is accepted now.
Is ''Quais '' the plural version of ''Qual'' ?
I think DuoLingo is having trouble recognizing English contractions. Already reported.
If in one of the previous sentences was right to say "qual a diferença" without the verb "é" (very strange for me), is it possible, here, to say "Quais as diferenças?" without "são", and if not, why not?