听力原文：W: Hi, Bill, how is it going? M: Oh, hi, Jan. I'm OK. How about you? W: You can probably tell just by looking at me. I'm really busy. Hey, what are you reading? M: A pretty interesting article. My biology professor assigned it, and I thought I just look it over. But I got really involved in it. It's about endangered species. W: That sounds pretty interesting. I'm getting frustrated with the two research papers I'm struggling with. And can you believe they are both due on the same day? M: That's tough. W: I'll get through it. So what's this you are reading? M: Well, it's basically about the choices conservationists are faced with. You know, these days when funding is so hard to come by. W: Wait a minute. Is the focus on biology or economics? M: Both. Conservationists don't have enough funding to save every endangered species in the world, so they have to decide based on what would be lost if a species became extinct. W: Can you give me an example of what you mean? M: Take for instance, two animals, the spotted owl and the tailed toad. The article says the toad is unique. It has no relatives. But there are a lot of varieties of owls. W: So, if that toad became extinct, we'd lose an important link in the chain of evolution, right? M: Exactly. But that isn't so for the owl. So for conservationists, it might be clear choice of which animal to save. W: I see. I am glad I don't have to make that kind of decision. Aren't you? (20)