Okay, so this is a flaw question. The hardest part about this question is not the stimulus, but rather, the abstract wording of the answer choices. When you come to a question with answer choices that have abstract wording, its best to move from wrong to right. Lets jump straight to the answer choices.
(B) is incorrect because the argument does not contain circular reasoning, or, as the answer choice states, the reasons given in support of the conclusion do not presuppose the truth of that conclusion. If you're having trouble understanding what "presupposing what the argument sets out to prove", means, click here for more information.
(C) is incorrect, and highly tempting (stupid abstract wording), because what its basically trying to say is that the evidence cited to show that a certain factor (not having equipment to monitor the patients O2 and Co2 levels) was absent when a certain result occurred (less people dying) does not show that the absence of that factor (not having the equipment) caused that result (less people dying).
In other words, not having the equipment does not show that less people dying occurred because of the absence of that equipment is what caused less people to die.
(Did you see how dumb that sounded?)
(D) is incorrect because the evidence is not inconsitent with any other information in the stimulus. The evidence (better training and equipment) is actually consistent. It would be easy to spot if it weren't, sort of like a paradox question.
(E) is incorrect because we don't have a third event so we don't even know what the heck this answer choice is talking about.
Lastly, (A) is the winner and your correct answer choice because the argument basically tries to say that having the equipment will not lead to significant cut in the fatalities simply because they already had a significant cut in fatalities when they had better training. You're probably asking yourself, "well wait, what if the new equipment, coupled with the better training leads to MORE lives being saved". And this, folks, is exactly what you should have asked yourself during this question. Answer choice (A) perfectly hits this point, in a more abstract sort of way.
Which brings me to my next point; never eliminate an answer choice because you don't know what it means, exactly. Only eliminate answer choices that you are positive cannot be correct, because once its eliminated, its hard to re-justify that it could be the answer choice.