Thanks for the question! Let’s take a look at the argument. We’re told that a certain species of bacteria will inevitably develop greater resistance to antibiotics, unless antibiotics eliminate it complete. Also, we know that there’s no antibiotics now that’ll eliminate the species completely. Let’s diagram this out:
Remember that we diagram “X unless Y” as ~Y —> X, so we have
~AEC —> BDGR
Now we’re told that ~AEC for all the antibiotics on the market now. So we can also conclude BDGR for all the antibiotics on the market now. And this is what (B) tells us, so (B) is the correct answer .
(E), on the other hand, is incorrect, although it is quite an attractive answer. Recall that we’re told that a bacterial species will inevitably develop greater resistance within a few years to any antibiotics against it. (E) tells us that species X is more resistant to at least some antibiotics that have been used against it than it was before those antibiotics were used against it. The problem with (E) is that it does rely on some assumptions. Let’s say that all antibiotics used against bacterial species X were used only a couple of seconds or minutes ago. Then, since it can take years for X to develop resistance, it’s not necessarily the case that X is more resistant at that point in time. (B), however, must be true based on the argument, as it follows logically, and so is a better answer. On the LSAT, we always have to find the best answer, not just pretty good answers. (E) is pretty good, but not as good as (B), because of the edge cases described above.
Hope this helps. Feel free to ask any further questions that you might have.
