A、Being overactive. B、Being mutant. C、Being selective. D、Being resistant. C女士说，标准模式认为白细胞对所有异己细胞都排斥，而在danger model中，白细胞则显示等待，选择对身

M: As a child, what kind of work did you think you’d be doing when you grew up?
W: A jockey, a dog trainer, a composer. But the only thing I’ve found, what I’m really creative is in science.
M: How did you find science?
W: I was a cocktail waitress in Davis, California, in 1972. One day, two professors from university started talking about animal mimicry, and I ask them "Why has no animal ever mimicked a skunk?" They were floored, and they decided that this question asking waitress should become a scientist.
M: What happened then?
W: For 9 months, they came to the bar and brought me all kinds of scientific articles. At their urging, I applied to graduate school and I got a Ph. D. I owe them my life.
M: When did you begin questioning the ideas that are the bedrock of immunological theory?
W: In graduate school, we learn that the immune system fights anything that isn’t part of your bodies, but that didn’t make sense to me. I wondered why we didn’t rejected the food we eat or the stuff in the air we breathe. But my professors all said "don’t worry about it."
M: So?
W: So I stopped worrying, but ten years later I met a brilliant young oncologist, He wondered about these questions, too, and we began trashing them out.
M: How does your danger model differ from the standard self/non-self model of the immune system?
W: The self/non-self-model believes that white blood cells kill anything that enters the body, but in the danger model. White blood cells wander around, waiting for an alarm, signaling that something is doing damage. And then they attack.
M: How did you arrive at your alternate model for the immune system?
W: It didn’t happen in a day. First, it took us a year to realize that a truly useful immune system would fight dangerous things and ignore harmless ones.
M: And the next?
W: Next we had to figure out how the white blood cells learn about the damage.
M: What is the value of your theory of the immune system?
W: Well, one of it is that I really believe we can use vaccination to cure, perhaps, eighty percent of all cancers. The danger model predicts that some simple changes could make anticancer vaccinations very effective.
M: But there is a lot of resistance to making those simple changes based on your theory, isn’t there?
W: The resistance isn’t really to the changes. It’s to the danger model itself. It’s partly fair. The danger model is new, but still, I don’t understand why they won’t try it on cancer in animals.
Questions 16-20 are based on the dialogue you have just heard:
16. Why did the woman end up doing a career in science?
17. What have the woman and her colleagues developed?
18. What are the white blood cells characterized by in the danger model?
19. What does the woman say about the value of her theory?
20. What does the woman suggest that we do about the changes based on the danger model?