Develop a theory about sea slugs that can be tested. Go to the ocean to observe the behavior of sea slugs. Obtain several sea slugs and conduct experiments with them. Review the research other scientists have done on sea slugs.
I gave my students this multiple choice question: A scientist plans to investigate the nervous system of sea slugs. What should the scientist do first?

Only one answer is correct among these 4 choices:
- Develop a theory about sea slugs that can be tested.
- Go to the ocean to observe the behavior of sea slugs.
- Obtain several sea slugs and conduct experiments with them.
- Review the research other scientists have done on sea slugs.

Could you tell me which one is correct?

Review the research other scientists have done on sea slugs.