Please choose the correct answer to the question: A scientist plans to investigate the nervous system of sea slugs. What should the scientist do first?

Answer1: Develop a theory about sea slugs that can be tested. Answer2: Go to the ocean to observe the behavior of sea slugs. Answer3: Obtain several sea slugs and conduct experiments with them. Answer4: Review the research other scientists have done on sea slugs.

Answer format: answer1/answer2/answer3/answer4
Answer: answer4