Plantings of cotton bioengineered to produce its own insecticide against bollworms, a major cause of crop failure, sustained little bollworm damage until this year. This year the plantings are being seriously damaged by bollworms. Bollworms, however, are not necessarily developing resistance to the cotton' s insecticide. Bollworms breed on corn, and last year more corn than usual was planted throughout cotton-growing regions. So it is likely that the cotton is simply being overwhelmed by corn-bred bollworms. In evaluating the argument, which of the following would it be most useful to establish? ['Whether plantings of cotton that does not produce the insecticide are suffering unusually extensive damage from bollworms this year', 'Whether corn could be bioengineered to produce the insecticide', 'Whether there are insecticides that can be used against bollworms that have developed resistance to the insecticide produced by the bioengineered cotton', 'Whether plantings of bioengineered cotton are frequently damaged by insect pests other than bollworms']