Ответ: 1. My grandparents were doctors (Мои прародители были врачами)

2. Mikhail wasn't at school yesterday (Михаил не был в школе вчера)

3. Roza was fourteen on May 1st.

4.  Were you late for school?

5. They weren't very good at tennis.

6. Was your sister a student at this school?

Объяснение:

1. Используем WERE, т.к множественное число

2. WASN't, т.к ед.число

4. WERE, мн.число

5. Из-за мн.числа

6. Ед.число