gwd-15-13

Q13:

Certain genetically modified strains of maize produce a powerful natural insecticide.  The insecticide occurs throughout the plant, including its pollen.  Maize pollen is dispersed by the wind and frequently blows onto milkweed plants that grow near maize fields.  Caterpillars of monarch butterflies feed 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?

1. Whether the natural insecticide is as effective against maize-eating insects as commercial insecticides typically used on maize are
2. Whether the pollen of genetically modified maize contains as much insecticide as other parts of these plants
3. Whether monarch butterfly caterpillars are actively feeding during the part of the growing season when maize is releasing pollen
4. Whether insects that feed on genetically modified maize plants are likely to be killed by insecticide from the plant’s pollen
5. Whether any maize-eating insects compete with monarch caterpillars for the leaves of milkweed plants growing near maize fields

答案为什么是C? 而不是D?