Question

Guillemots are birds of Arctic regions. They feed on fish that gather beneath thin sheets of floating ice, and they nest on nearby land. Guillemots need 80 consecutive snow-free days in a year to raise their chicks, so until average temperatures in the Arctic began to rise recently, the guillemots' range was limited to the southernmost Arctic coast. Therefore, if the warming continues, the guillemots' range will probably be enlarged by being extended northward along the coast.
Which of the following, if true, most seriously weakens the argument?

• A. Even if the warming trend continues, there will still be years in which guillemot chicks are killed by an unusually early snow.
• B. If the Arctic warming continues, guillemots' current predators are likely to succeed in extending their own range farther north.
• C. Guillemots nest in coastal areas, where temperatures are generally higher than in inland areas.
• D. If the Arctic warming continues, much of the thin ice in the southern Arctic will disappear.
• E. The fish that guillemots eat are currently preyed on by a wider variety of predators in the southernmost Arctic regions than they are farther north.

Hint:

When an argument predicts a future outcome based on a single changing factor, the strongest way to weaken it is to show that the same change also has a negative effect on another, equally critical factor that the argument has ignored.

Answer 1

The Correct Option is D

Step 1: Understanding the Argument
The argument predicts that global warming will allow guillemots to expand their habitat northward.
Premises: \[\begin{array}{rl} \bullet & \text{Guillemots need 80 consecutive snow-free days for breeding.} \\ \bullet & \text{This has historically limited them to the southern Arctic.} \\ \bullet & \text{Arctic warming is increasing the number of snow-free days further north.} \\ \end{array}\] Conclusion: The guillemots' range will extend northward.
Assumption: The argument assumes that the only critical factor currently limiting the guillemots' range is the number of snow-free days, and that all other necessary conditions for their survival (especially their food source) will become available in the newly warmed northern regions.

Step 2: Analyzing the Task
To weaken the argument, we need to find a statement that shows that even with more snow-free days in the north, the guillemots will be unable to expand their range. This usually involves identifying another necessary condition for survival that will be negatively affected by the warming trend.

Step 3: Evaluating the Options
(A) Occasional bad years with early snow do not refute a long-term trend of range expansion. The argument is about the probable change in the overall habitat range, not about guaranteed success every single year.
(B) The presence of predators in the new northern range would pose a challenge, but it does not automatically mean that range expansion is impossible. The guillemots already face predators in their current range.
(C) This statement describes where guillemots nest, which is consistent with the argument's conclusion that their range will extend "northward along the coast." It doesn't weaken the argument.
(D) This option attacks a crucial, unstated condition for the guillemots' survival. The text explicitly states that they "feed on fish that gather beneath thin sheets of floating ice." This ice is essential to their feeding strategy. If Arctic warming causes this ice to disappear, their food source will be eliminated. The disappearance of their food source would make the region uninhabitable, regardless of how many snow-free days there are for nesting. This directly contradicts the idea that the area will become a larger, more viable habitat for them.
(E) This suggests that moving north might actually be beneficial by reducing the variety of predators. This would strengthen, not weaken, the argument for northward expansion.
Step 4: Final Answer
Option (D) is the correct answer because it points out a devastating consequence of the warming trend that the argument overlooks. The same warming that provides more snow-free nesting days also destroys the birds' feeding grounds, making the expansion of their range impossible.