Duo needs to get rid of this "you all" thing. "Look at the fruit" is a perfectly good translation here. That is what would most likely be said in English, and it would be absolutely correct, no matter how many people were being addressed. When translating from English to Swahili, if the context makes it clear that multiple persons are being addressed, then fine, insist on an m- prefix or an -eni suffix as appropriate, to indicate the "plural you."
working toward eliminating it. Bothered me like no one's business when I first tried the course. We're still coming across sentences like these that haven't been corrected yet. Keep reporting! (and by that I mean start a discussion if you can, those are much easier to track than reports, which are upwards of 2000 per lesson at this point)