Используем Present Perfect (have/has + V3) и вставляем слова 'just', 'yet', 'already' в правильные места.
Ответ: 1. I haven't finished this exercise yet. 2. My sister has just arrived home. 3. Holly and Jack have already eaten lunch. 4. My mum has just got back from work. 5. Have you seen that film yet?