Genitive

a

Exercises

https://www.englisch-hilfen.de/en/exercises/nouns_articles/apostrophe_s2.htm

https://www.englisch-hilfen.de/en/exercises/nouns_articles/apostrophe_s.htm

More Exercises on Genitive Case

http://www.hseidensticker.de/unit0/sgenplur.htm

https://www.tolearnenglish.com/exercises/exercise-english-2/exercise-english-11212.php

http://suz.digitaleschulebayern.de/english/grammar/saxong3.htm