11. When the teacher came into the classroom, the children

11. When the teacher came into the classroom, the children were talking.

Пояснение: Past Continuous описывает действие, которое происходило в прошлом, когда другое действие (teacher came) прервало его. Дети разговаривали в тот момент, когда учитель вошел.

Ответ: When the teacher came into the classroom, the children were talking.