Why introduce new concepts in areas we have no way of knowing?
To clarify what I mean, frequently in "choose all correct translations" questions, there will be one correct answer that we know is correct, because we have been taught so, and one answer that we have no chance of knowing, because it has not been taught or properly introduced. The most common example of this would be the several variations of "Dw i," such as "Rydw i" and "Dwi." Now this alone isn't so bad, but then we also have things like "Wyt ti," meaning "You (singular) are" when we'd only been formally introduced to "Dych chi." Another example I just came across was apparently an alternate spelling for the noun "orange." The answer was "orains," which according to google translate is Scots Gaelic. Every translation source and Welsh-English dictionary I can find online only lists "oren" as a correct translation for "orange." What gives?
I can completely sympathise with you and I have brought this to the attention of others members of the dev. team before. Hopefully it will get sorted; I know that www.duolingo.com/rmcode is encouraging users to write on his feed directly so he's made aware of the problem - perhaps drop him a message too?
Oraens is, strictly speaking, the actual fruit, but nowadays, many Welsh speakers will just say oren.
While the Welsh course goes perhaps a bit further in this regard than many other courses, springing sentences on you that you can't be expected to know because you haven't learned all the words or grammar yet is something I've often seen before -- it seems to be part of "the Duolingo way". Not as a general rule, but as something that comes up every now and then.