www.softschools.com/quizzes/grammar/possessive_nouns/quiz327.html - v tomto cvičení doplňujete buď ´s v jednotném čísle, nebo jenom ´ v množném čísle
www.liveworksheets.com/w/en/english-second-language-esl/166277
www.ego4u.com/en/cram-up/grammar/nouns/exercises?04
www.liveworksheets.com/w/en/english-second-language-esl/123909
www.englishexercises.org/makeagame/viewgame.asp?id=12056