Помогите, пожалуйста:
Explain the usage of the Past Perfect Tense in the following sentences:

1.Mary said (that) she hadn’t done her homework. 2. The policeman asked
me if I had seen the accident. 3. The sick man felt better after he had taken
his medicine. 4. When we reached the station, the train had left. 5. It was
five to ten in the morning. The exhibition had not opened yet, but all the
preparations for the opening ceremony had been made, and a lot of people,
who had come to watch it, were standing outside and waiting. 6. Many
reporters wanted to talk to the winner, but he was too tired to talk. He had
run a long race and wanted to have a rest. He was very happy, because it
was his first real victory. He had never taken part in such an outstanding
event before.

Какой это класс??Просто чтобы я знала)