Ответ:

Ex. 3

Объяснение:

1. We have already cleaned our room. When the mother came, we had already been cleaning our room for 10 minutes.

2. They have lived in this flat since 1990.

3. The workers have been working for half an hour.

4. John has been laying the foundation for 3 days.

5. The architect has already designed the house.

6. She said she had been living in this city for 20 years.