Final answer:
The student found the solar system topic interesting.
Explanation:
Useful would be the most appropriate choice. The topic of the solar system is not depicted as 'unhappy' or 'useless' based on the context provided. The student found it 'interesting,' which aligns more with 'really' or 'useful.'
Learn more about Solar System here:
https://brainly.com/question/13899929
