After singular nouns , add -'s e.g. This is Sue’s bag. [the bag belongs to Sue]
when the noun is plural but doesn’t end in 's' e.g. men’s toilet
After plural nouns, add -s' e.g. Is that the girls' bedroom? [the bedroom belongs to more than one girl]
of can also be used to show possession
e.g. the name of the book, a friend of mine, the teacher of the class
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