Whose ball is this?
It's Mark's ball.
Whose rulers are these?
They're Susan's rulers.
Whose dog is this?
It's Susan's dog.
Whose glasses are these?
They're Mark's glasses.
Whose cat is this?
It's Mark's cat.
Whose dress is this?
It's Susan's dress.
Whose crayons are these?
They're Mark's crayons.
Whose doll is this?
It's Susan's doll.
Whose cap is this?
It's Mark's cap.
Whose books are these?
They're Mark's books.
Whose apple is this?
It's Susan's apple.