That's because "собаки" is both the nominative plural form of 'dog' and also the genitive singular form of 'dog'. I added a new hint to make it less confusing for you :) But also, try to remember that genitive case follows "нет", so "Mom does not have dogs." would translate to "У мамы нет собак."
Yes, I think I am starting to understand the Russian way of thinking. in french it it easier to understand. it would literally translate :as:de la mere pas de chien., thus the genitive case. I am studying Russian on the english basis though I am a French-speaking Swiss living in South America since 1992. I am 76.
yes, you are correst, NET must be followed by the genitive case. I just realized it yesterday. It's like in German, where " durch - fuer - gegen - ohne - um - must be followed by the accusative, wegen, trotzdem etc. by the genitive and aus - bei, mit ,nach, seit ,von, zu ,either by the dativ or accusative according to the sentence. So I will have to look for these Russian terms and see what case they need and learn them by heart like I did with German when I was in primary school in Switzerland 67 years ago ( i am from the french-speaking part of Switzerland).
These comments are great, but Duolingo doesn't teach what genitive cases are. Or anything about cases. The sections are labeled as such but there are no explanations. Duolingo may be great as a refresher or vocabulary teacher, but it fails to truly teach a language if it doesn't describe what's going on.