Ответ:
1. My keys were found (by somebody).
2. This vase was broken (by somebody).
3. My pen was borrowed (by somebody).
4. Milk tea has been drunk (by us).
5. This book was written in the 19th century (by him).
Объяснение:
То, что в скобках, писать не обязательно, я написала на всякий случай.