Critical Reasoning

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.

D

AbeNeedsAnswers wrote: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.

D

Conclusion: If warming continues, the guillemots' range will be enlarged
Premise: Guillemots require 80 consecutive snow-free days to raise their young; temperatures are rising
;
If we' want to weaken argument, we want to see some sort of unforeseen negative consequence of the temperature increase. We're told that the fish they eat gather beneath thin sheets of ice. If that ice disappears in response to warming, it will, presumably, effect the guillemots access to these fish. The answer is D