Answer:
1. Researchers have been investigating the problem for 15 years.
2. This issue was raised during the seminar.
3. It is assumed that the management knows what is happening and will therefore intervene if there is a problem.
4. Schools cannot altogether eliminate the problem of truancy.
5. The number of staff has been reduced lately.
6. It was very difficult to establish exactly what happened.
7. House prices have a tendency to fluctuate.
8. A potential solution was proposed two years ago.