4. Use the perfect infinitive of the verbs in brackets with a suitable modal verb.

Решение:

1. The instructions were in Italian. I translated them into Russian for him. - You (not translate) them. He knows Italian.
   You must have misunderstood them. He knows Italian. (Выражение предположения о прошлом действии, которое могло привести к ошибке).
2. I've never seen a London cab. - You (see) one! You've been in London a week already!
   You must have seen one! You've been in London a week already! (Выражение уверенности в прошлом действии).
3. Look at this beautiful painting! Only a very great artist (paint) such a picture!
   Only a very great artist could have painted such a picture! (Выражение возможности/способности в прошлом).
4. Nonsense! A child of five (paint) it with his eyes shut.
   Nonsense! A child of five could paint it with his eyes shut. (Выражение возможности/способности в прошлом).
5. You (prepare) for the exam more thoroughly to pass it.
   You should have prepared for the exam more thoroughly to pass it. (Выражение сожаления о несовершенном действии в прошлом).

Ответ: must have misunderstood; must have seen; could have painted; could paint; should have prepared.