병 can also be translated as illness or disease. If the answer is "Is it a bottle?", "Is it an illness?" should not be marked as incorrect.
I did the same thing
That's because Koreans have stopped using Hanja. This sentence, technically, can be rewritten as "瓶이니" or "病이니". Both answer should be accepted. By the way, we may use "疾病"(질병) to avoid confusion.
Damn... Yeah, I fell onto the same situation! "병이니?" also has the meaning of "Are you sick/ill?"
Duolingo, CURSE YOU FOR DOUBLE MEANINGS!!!
Are you sick? Are you crazy/ not yourself??? Double meaning????
Or maybe it is a bird?