Whose computer is this?

It's Tina's. It's her computer. It's hers.

Whose camera is that?

It's Bob's. It's his camera. It's his.

Whose watch is this?

It's Tony's. It's his watch. It's his.

Whose skateboard is that?

It's Bill's. It's his skateboard. It's his.

Whose football is this?

It belongs to Paul and Ann. It's their football. It's theirs.

Whose alarm clock is that?

It's Pat's. It's their alarm clock. It's theirs.