TOEFL Listening: ETS-TOEFL听力机经 - DK1JT_WJA74X4WK9P$

What is the main purpose of the lecture? A. To explain how biologists learned that not all mutations to a species are beneficial to the species B. To explain why biologists' views about evolutionary adaptations have recently changed C. To explore the advantages and disadvantages of toxins as a defense against predators D. To discuss efforts to find ways to counteract a powerful toxin