Выделено жирным первое пропущенное слово в каждом предложении.
1 her, mine
2 their car and you gave them yours.
3 his documents and they gave him theirs.
4 our address and she gave us hers.
5 her greenhouse and I showed her mine.
6 us new pigeons and we showed him ours.
7 their fairy tale and she told them hers.
8 me about her new pet and I told her about mine.
9 my puppy and they brought me theirs.
10 our sandcastle and we ruined his.