‘whose’
Look at the pictures and use the word ‘Whose’ in the question.
Whose ball is this? It's her ball
Look at the pictures and use the word ‘Whose’ in the question. (I and Lucy)
Whose watch is this? It's our watch
Look at the pictures and use the word ‘Whose’ in the question. (Tom)
Whose umbrella is this? It's Tom's umbrella