Ответ:

1. her

2. yours

3. ours

4. him

5. theirs

6. his

7. your

8. mine

9. her

10. their

Объяснение:

Правило хорошо объяснено тут: https://forum.duolingo.com/comment/3158863/%D0%9F%D1%80%D0%B8%D1%82%D1%8F%D0%B6%D0%B0%D1%82%D0%B5%D0%BB%D1%8C%D0%BD%D1%8B%D0%B5-%D0%BC%D0%B5%D1%81%D1%82%D0%BE%D0%B8%D0%BC%D0%B5%D0%BD%D0%B8%D1%8F-%D0%B2%C2%A0%D0%B0%D0%BD%D0%B3%D0%BB%D0%B8%D0%B9%D1%81%D0%BA%D0%BE%D0%BC-%D1%8F%D0%B7%D1%8B%D0%BA%D0%B5-%C2%ABYour%C2%BB-%D0%B8%D0%BB%D0%B8-%C2%ABYours%C2%BB