Ответ:
1. Were the boys at the park yesterday evening? No, they weren't
2. Was Mary at the zoo last Sunday? Yes, she was.
3. Was Juan in London last summer? No, he wasn't.
4. Were the girls at a party yesterday afternoon? No, they weren't.
5. Was Cara at the theatre last night? No, he(он) или she(она) (просто непонятно мальчик или девочка) wasn't.