A、The researchers had made some mistakes. B、The researchers repeated the experiment many times. C、E. coli was almost completely

Now, listen to Part Two of the interview.
M: What was shocking was the following day the E. coli experienced this population explosion. All of a sudden their numbers were up to 500% higher than they had been before.(6)So they just really started multiplying, really out of control. And at first the researchers thought they had made some sort of mistake. They repeated the experiment, and they saw the same thing happen again.
W: That’s really unexpected. So I assume this new population is much more likely to be resistant to the antibiotics that were used.
M: It is.(7)And what the researchers found was that, just like what happens with one drug, with a couple drugs it still left a few bacteria left in this population that were really good at fighting these antibiotics. In fact the bacteria seemed to have multiple genes for pumping out these antibiotics.(8)So these antibiotics, you know, get into the bacterial cell and the bacterium usually dies, but there are some bacteria that were very good at just basically pumping this antibiotic right back out again. And those were the ones that survived. And even in the presence of two antibiotics they just started to thrive after about a day because the antibiotics had wiped out all their competition. So all of a sudden they had access to all these resources, all this food that they didn’t have access to before. And that they’re basically growing out of control because the drugs aren’t having any effect on them.
W: And so the two examples of really nasty diseases that you mentioned earlier, both HIV and MRSA, in which this synergistic method is used quite a bit. I mean they’re really difficult-to-treat diseases. If we start not using this method, are there any alternative methods for treating them?
M: Well,(9)one thing the researchers suggest is instead of hitting bacteria with two drugs at the same time we should alternate the drugs. So use one drug one day, wipe out most of the population, and maybe you’ll have some leftovers that are resistant to that drug, but then you hit it with a different drug the next day, and maybe that will wipe out the remainder.
W: I get it. This idea is sort of mix things up so much that bacteria really don’t have a chance to become resistant. That’s certainly one possible way to go.
M:(10)All this stuff is in test tubes right now, so it sort of remains to be seen whether this is actually happening in the human body. But it is a really powerful warning sign for a lot of these multi-drug treatments.
W: Indeed. Well, thank you, Dave, for sharing with us such interesting information.
M: My pleasure.
This is the end of Part Two of the interview.
Questions 6 to 10 are based on what you have just heard.
6. What was shocking about the experiment of E. coli?
7. What did the researchers find about the new population of E. coli in the experiment?
8. According to the interviewee, how do bacteria develop resistance?
9. According to the researchers, what should doctors do to treat diseases like HIV?
10. According to the interviewee, what is the problem with the research?