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47 Certain genetically modified strains of maize produce a powerful natural insecticide. The insecticide occurs
throughout the plant, including its pollen. Maize pollen is dispersed bythe wind and frequently blows onto
milkweed plants that grow near maize fields. Caterpillars of monarch butterfliesfeed exclusively on milkweed
leaves. When these caterpillars are fed milkweed leaves dusted with pollen from modified maize plants, they die.
Therefore, by using genetically modified maize, farmers put monarch butterflies at risk.
Which of the following would it be most useful to determine in order to evaluate the argument?
(A) Whether the natural insecticide is as effective against maize-eating insects as commercial insecticides
typically used on maize are
(B) Whether the pollen of genetically modified maize contains as much insecticide as other parts of these plants
(C) Whether monarch butterfly caterpillars are activelyfeeding during the part of the growing season when
maize is releasing pollen
(D) Whether insects that feed on genetically modified maize plants are likely to be killed by insecticide from
the plant's pollen
(E) Whether any maize-eating insects compete with monarch caterpillars for the leaves of milkweed plants
growing near maize fields
Argument Evaluation
Situation Monarch butterfly caterpillars die when fed milkweed leaves dusted with the pollen of
certain genetically modified strains of maize.A natural insecticide occurs throughout the
maize plant and in its pollen, which blows onto milkweed growing near maize fields.
Caterpillars of monarch butterflies eat onlymilkweed leaves, so farmers who use this
genetically modified maize are endangering monarch butterflies.
Reasoning What woidd it be most useful to know in evaluating the argument?We knowthat the
caterpillars eat onlymilkweed leaves, butwedo not knowwhen, in the course of their
development, theydo so. Monarch butterflies would be at riskonlyif the caterpillars
were to eat the milkweed leaves when those leaves had maize pollenon them. So it
would be useful to know if the caterpillars eat milkweed leaves when maize pollen is
likely to be present.
A Theargument addresses whether farmers put monarch butterflies at riskbyusing genetically
modified maize. The effectiveness of the natural insecticide that maize produces, relative to other
insecticides, is not relevant to determiningwhether monarchbutterflies are being endangered.
B Theamount of insecticide in the restof the plant, asopposed to in its pollen, has nothing to do
withwhether the use of the maize puts monarch butterflies at risk. All that matters is the amount
of insecticide in the pollen, andweknow that this is sufficient to kill the caterpillars.
C Correct. This question properly identifies something that it would be useful to knowin
evaluating whether monarch butterflies are actually at risk—that is, whether caterpillars will be
eating milkweed leaves whenthose leaves are likely to have pollen on them.
D Since the issue at hand iswhether farmers are endangering monarch butterflies, the question of
the maize pollen's impact onother insects—that is, those thatfeed onmaize—is irrelevant.
E Competition from maize-eating insects attracted to the area by the planting ofmaize might
affect the monarch butterfly population, but simply knowing that such insects might compete
with the caterpillars for milkweed leaves does not give any information onwhether they would be
able to compete successfully for those leaves.
The correct answer is C. |
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发表于 2013-3-10 00:01:11
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