Возможны неточности, но вот:
1.
1)had seen,visited
2) learned, had gone.
3) did,had begun
4)said, had gone
5) had realize, made
6) wrote, had come
7) ate, had come
2.
1)nobody had opened the door
2)I had a headache.
3)
4)I hadn`t allowed to drive a car.
3.
When I read the letter I had throw it away.
He had bought a car as soon as he pasted his driving test.
I had taken the book back to the library when i finished reading it.
I had gone at home when I spent all my money.