Complete the following sentences using past perfect.
1. My sister realized she (forget) her ticket when we got to the stadium.
2. When we got to the airport the plane (leave).
3. When I got to his house, my cousin (wake up).
4. We (hear) about the accident by the time Jessy got home.
5. The party (start) when I arrived.
6. I (eat) when I came to the university.
7. She (study) when she took the test.
8. They (buy) the tickets when they went to the concert.