A、Because every species becomes extinct. B、Because humans beings are powerful enough to kill other species. C、Because of over-po

W: Professor Marnes, I wonder if you can fill me in on your lecture last Friday. I had to attend a scholarship award ceremony.
M: Oh well, congratulations. I hope you were rewarded handsomely!
W: Well, every bit helps. So, about your lecture, I understand you were talking about extinctions.
M: Yes. Well, the crux of my talk was just that we tend to think of extinction as a dramatic event, but most species die out over quite a period of time.
W: Why do they die off? I thought they were continuously improving themselves. Natural selection, I think you once mentioned.
M: Ah, but you see while there is natural competition between the species, what determines which species survive is largely by chance.
W: I don’t get it. Why do species bother competing?
M: Well, there are short-term advantages. But many species also are helped by others. For example, the common housefly and cockroaches might have died off years ago if not for humans.
W: But you’re not saying that humans are so successful merely because of chance?
M: To a certain extent, humans were initially lucky enough to have the right weather conditions and a lack of predators, but now, of course, we survive by ingenuity!
W: So we may never become extinct.
M: No, because we may be in a crash course to extinction by our continuous exploitation of the environment. We are a relatively young species and our time is not yet overdue.
W: But there are 6 billion of us!
M: Yes and there’re many more houseflies too! Each with the capacity to spread one disease from one person to another in a fast period of time.