Ответ:

1. But he hasn't learnt English yet.

2. Stuart has done his homework for two hours.

3. He has already cleaned the garden.

4.  Melanie has a lot of homework, too. She has done her homework since 4 o'clock.

5. She hasn't watered the flowers in the house yet.

6. Daniel has already learnt the new verbs,

7. Melanie has just drawn the picture.

8. Daniel and Melanie have already finished everything.