4. These tourists have never taken an eco-tour to the national park before.
→ This is the first time these tourists have taken an eco-tour to the national park.

5. If Marie doesn't get good marks, her parents won't let her attend the summer camp.
→ Unless Marie gets good marks, her parents won't let her attend the summer camp.

6. This photo reminds me of the time I climbed a mountain with my friends.
→ This photo makes me think of the time I climbed a mountain with my friends.

7. Seeing a tribal dance show was more interesting than other activities during the trip.
→ Seeing a tribal dance show was the most interesting activity during the trip.

8. At the time the bear appeared at the campsite, everyone was putting up tents.
→ The bear appeared at the campsite while everyone was putting up tents.

9. They were excited about exploring the ancient site of Machu Picchu.
→ They found it exciting to explore the ancient site of Machu Picchu.

10. The last time that singer gave a performance was five years ago.
→ That singer hasn't given a performance for five years.