It is difficult to keep deep wounds free of bacteria. Even strong antibiotics fail to kill the bacteria that live in such wounds. However, many physicians have succeeded in eliminating bacteria from deep wounds by packing the wound with a sweet substance like sugar.

Which one of the following, if true, most helps to explain why treating deep wounds with sugar as described above is successful?

[A]. Bacteria that live in deep wounds thrive in a moist environment, and sugar has a dehydrating effect.
[B]. Sugar that is nearly pure is readily available for use in medical treatments.
[C]. Many kinds of bacteria can use sugar as a nutrient and will reproduce rapidly when sugar is available to them.
[D]. Some foods that contain sugar can weaken the effects of certain antibiotics.
[E]. Strong antibiotics were developed only recently, but the use of sugar as a treatment for wounds dates back to ancient times.
Answer: A

It’s tough to pre-phrase an answer to this one; you simply need to attack the choices in search of an explanation as to why packing a wound with sugar would so successfully kill those hardy and ubiquitous bacteria. And you needn’t search long: If sugar makes a wound dry and if bacteria like moisture, as (A) states, then it’s not surprising that a sugar environment tends to spell R.I.P. for bacteria.

(B) So sugar is available for use. But how would one use it? Why would it be successful?

(C)’s phenomenon creates a paradox, not resolves one. We’re trying to figure out why sugar in a wound kills bacteria, not how it might provide an environment in which they thrive.

(D) deals with foods that contain sugar, which is far removed from the treatment described. And in any case, if sugar were to weaken an antibiotic (assuming that such a drug were prescribed for a wound), that would be harmful rather than helpful. Both (C) and (D) give us more or less the opposite of what we want.

(E) is unnecessary background information. What does the long-time use of sugar on wounds have to do with why it has the effect it does?

When trying to strengthen or justify an argument or process, beware of answer choices (such as (C) and (D), here) that tend to do the opposite of what you seek. We call such choices “au contraire” and they are common on the CAT.

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