4. We have made great progress in industry, science and medicine.

 great progress has been made in industry, science and medicine

5. Sam killed a lion last week.

 A lion was killed by Sam last week

6. You must hand in your report before the end of this month.

 Your report must be handed in before the end of this month

7. I had just finished the job when the factory closed.

 The job had just been finished when the factory closed

8. No one has opened that box for the past hundred years.

 That box hasn't been opened for the past hundred years