Duolinguo seems to be very rigid in what they accept as correct responses/answers. For instance, if as a native or proficient speaker of English one changes the structure of the Swahili sentence in the English translation or the sequence of the words (vis-a-vis the sequence in Swahili) to align with how one would actually say them naturally in English one's response is marked incorrect even though one is actually correct. I've been having an ongoing battle with one of their moderators about writing my answer as "500 thousand" instead of "500,000" when asked to translate "laki tano" into English in one of the exercises. As if it made any difference! The object of these exercises is to test comprehension - & my response clearly indicates I comprehend "laki tano" - yet they make it seem like there is any difference between "500" and "five hundred". Yet in other exercises they accept both 12 and "twelve". Yeah, I know I'm venting, but that because I'm pissed that they don't seem to be taking learners' feedback seriously enough!