3)
2. Rosalie was cooking dinner when she cut her finger. (длительное действие, прерванное другим)
3. Lizzy and Nadia were playing basketball at 5 o'clock yesterday. (длительное действие в определенный момент в прошлом)
4)
2. Were you having lunch at 2 o'clock yesterday afternoon?
Yes, I was.
3. Were you talking on phone at 8 o'clock yesterday evening?
No, I wasn't. I was having dinner.
4. Were you watching DVD last Saturday morning?
Yes, I was.