Try and read through the below discussion. i hope it helps.
If 'La ragazza mangia la frutta.' is correct and 'La ragazza mangia frutta.' is also correct, shouldn't both answers be correct whichever you use? No matter if it's left out in the real world in Italian. The lessons need to be more consistent throughout the app.
I have noticed many times that I have been wrong because I left 'Io' out one time for a lesson containing 'bevo'. But then another time it is not required and I add it, and get it wrong.