The algorithm accepts "mom" automatically every time when "mother" is accepted, it should have worked.
However, I have to say that if we could reject it, we would. "matka" is considered a rather formal word. It's not only more formal than "mom", but seems more formal than "mother" as well; there's just no better translation.
Thanks... After I posted this I noticed in some other exercises it uses "mama" for "mom", and "matka" for "mother".
Why is kapelusze rather than kapeluszy in plural? Isn't kapelusz a masculin nom?