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