4. — _______ he _______ (solve) the task yet? — No, he _______. He _______ still _______ it. — How long _______ he _______ (solve) it? — He _______ (solve) it for half an hour.

Решение:

1. Has he solved (solve) the task yet?
2. — No, he hasn't solved. He is still solving it.
3. — How long has he been solving (solve) it?
4. — He has been solving (solve) it for half an hour.

Ответ: Has solved; hasn't solved; is still solving; has been solving; has been solving.