TOEFL Listening: ETS-TOEFL听力机经 - 5U5E4AMAN0O4Y5FAP$

What is the main purpose of the lecture? A. To introduce a theory about why marine animals form symbiotic relationships B. To discuss the application of categories of symbiosis to marine animals C. To question research done on the relationship between sea butterflies and amphipods D. To explain how the categories of symbiosis were developed by researchers