8. they having a housewarming party at this time last Sunday? — Yes, they / No, they

8. they having a housewarming party at this time last Sunday? — Yes, they / No, they

Согласно грамматике английского языка, необходимо вставить вспомогательный глагол перед подлежащим, чтобы образовать вопрос в Past Continuous (прошедшее продолженное время).

В данном случае, подлежащее - they, поэтому используем вспомогательный глагол were.

they having a housewarming party at this time last Sunday? - Were they having a housewarming party at this time last Sunday?

Yes, they / No, they - Yes, they were / No, they weren't.

Ответ: Were they having a housewarming party at this time last Sunday? — Yes, they were / No, they weren't