Ответ:
I.
1. I had had breakfast before I went to school.
2. He went to meet his friends after he had done his homework.
3. By 8 o'clock the rain had stopped.
4. Alice was late because she had missed the bus.
5. She went to the post office after she had written the letter.
II.
1. Ann had done her homework before Mary phoned her.
2. My father repaired his car after I had come home from school.
3. We had visited our Granny by 6 o'clock.
4. When he entered the house he understood that somebody had already been here.
5. After he had written a letter he went to the post office.