Is ''Quais '' the plural version of ''Qual'' ?
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.
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?
Yes, it is possible! It's informal, but it's okay to remove são in this context. It just doesn't add much information to the sentence.
Please don't assume that you can remove the verb to be in every sentence because that would be weird XD
I think DuoLingo is having trouble recognizing English contractions. Already reported.
Que / quais.. Same thing?