The Plurals lesson should come after learning the singular forms
Duolingo is a great way to learn Italian, but why does the Plurals lesson include words where there was no previous lesson for their singular forms? E.g. it teaches the word for "horses" but not the singular word for "horse". Why do it that way?
Duolingo's method is quasi-immersion, where you're learning from context. This means you get less repetition (unless you need it), and you can progress more quickly and more naturally.