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