This is another sentence that could go either general or specific: "Tigers and wolves" or "The tiger and the wolf."
Why is "a tiger and a wolf" wrong?
I think because there is not "sebuah" word in that sentence. "A" is meaning "sebuah" in Indonesia
The Duolingo staff are seriously negligent with loading up all the possible responses to this question. Both "Tigers and wolves." and "A tiger and a wolf." should certainly be included.