Ответ:

  1. His flat is spacious.
  2. Is Ruth your sister?
  3. This camera isn't mine.
  4. This little puppy isn't ours.
  5. Tina and Susan are my friends.
  6. What's your phone number?
  7. Is this skateboard his?
  8. Their house is very modern.
  9. Are these books hers?
  10. What is his address?

В предложениях 30, 31 и 34 без контекста возможны и другие местоимения из предложенных вариантов: her в №30, her в №31 и her в №34. Выбор зависит от того, о ком говорится.