Evaluate

Lyme disease is caused by a bacterium transmitted to humans by deer ticks. Generally, deer ticks pick up the bacterium while in the larval stage by feeding on infected white-footed mice. However, certain other species on which the larvae feed do not harbor the bacterium. If the population of these other species were increased, more of the larvae would be feeding on uninfected hosts, so the number of ticks acquiring the bacterium would likely decline.

Which of the following would it be most important to ascertain in evaluating the argument?

A. Whether populations of the other species on which deer tick larvae feed are found only in areas also inhabited by white-footed mice
B. Whether the size of the deer tick population is currently limited by the availability of animals for the tick's larval stage to feed on
C. Whether the infected deer tick population could be controlled by increasing the number of animals that prey on white-footed mice
D. Whether deer ticks that were not infected as larvae can become infected as adults by feeding on deer on which infected deer ticks have fed
E. Whether the other species on which deer tick larvae feed harbor any other bacteria that ticks transmit to humans

Plan: Increase the population of food sources that do not harbor the bacterium associated with Lyme disease.
Conclusion: The number of ticks acquiring the bacterium will decline.

Rephrase the answer choices as STATEMENTS without the word whether.
The correct rephrase will either STRENGTHEN or WEAKEN the conclusion that the number of infected ticks will decline.
Let the current tick population be as follows;
100 uninfected ticks, 100 infected ticks.

B, rephrased:
The size of the deer tick population is currently limited by the availability of animals for the tick's larval stage to feed on.
Since the tick population currently lacks sufficient food to grow, doubling THE AMOUNT OF UNINFECTED FOOD could simply double THE NUMBER OF UNINFECTED TICKS, as follows:
200 uninfected ticks, 100 infected ticks.
Since the number of infected ticks would remain 100, the conclusion that there will be a decline in the number of infected ticks is WEAKENED.

The correct answer is B.

Because this is an EVALUATE CR, the correct answer will have a LOT to do with scope and the conclusion.

Conclusion: If the population of these other species were increased, more of the larvae would be feeding on uninfected hosts, so the number of ticks acquiring the bacterium would likely decline.

Simplified Conclusion: More species + more feeding = fewer ticks with B

The correct answer must address the INVERSE proportion claimed by the author: species/feeding goes up, and ticks with B does down.

(A) discusses where these species are "found" -- this is NOT what the conclusion focuses on. If the other species are found ONLY with mice, or only SOMETIMES with mice does not have a strong bearing on the conclusion one way or the other.

(B), however, DOES have an effect. What if there WERE more species, as the conclusion says? Then there would be MORE availability of animals for feeding, so the conclusion that there would be "fewer ticks" would be significantly impacted. In fact, there would probably be MORE, implying a directly proportional relationship between other species' population and deer ticks.

That is how we know (B) is correct: when we answer it one way, it has a HUGE impact on the conclusion. (A) is incorrect because the conclusion could still be true even if we answer it both ways.