TOEFL Listening: TPO-TOEFL阅读TPO - FA772UEO2T1O5G11N$

What is the main purpose of this passage? A. To explain the concept of symbiosis by expanded descriptions of its principal types B. To make a comparison between human relationships and symbiotic interactions in the natural world C. To demonstrate the unforeseen benefits of natural processes that at first seem wholly destructive D. To argue that parasitism is a problem that can be solved by scientific intervention