Do the rings have to be articulated? Or, more broadly, when a noun has a genitive/dative noun responding to it, does it have to be articulated?
I learned that with the (possessive) genitive, yes, the noun must have the "definite" article. Think of it as a reinforcement that they are not just any rings, or rings in general, but specifically those that belong to the mothers.
Duolingo is making me start to doubt my command of my mother tongue of English.