Вот правильные варианты заполнения пропусков:
- I thought he already had gone home.
- I hadn't seen him after we had met at the concert.
- He had left the house before I had time to ask him anything.
- After he had spent some days in Paris he felt lonely and wanted to return home.
- He spoke a language we never had heard before.
- When the rain stopped, I looked out of the window.
- The telegram came some minutes after he had left.
- She thought that Tom and Lanny had quarrelled.
- The girl was glad that she had found a seat near the window.
- He remembered that he hadn't rung her up in the morning.
- By the time the train reached the city, he had made friends with many passengers.
- When my uncle left, he hurried to the station to book a ticket.