It is crucially important to farmers that the herbicides they use to control weeds do not damage their crops. One very effective herbicide is safe for corn, but soybeans are damaged even by the herbicide' s residue, which remains in the soil more than a year after the herbicide is applied. Soybeans and corn are not sown together in the same field; nevertheless, most farmers are reluctant to use the herbicide on their corn. Which of the following, if true, provides the strongest justification for the farmers' reluctance? ['The demand for soybeans is growing faster than is the demand for corn.', 'To maintain the nutrients in the soil, corn and soybeans are often planted in a field in alternate years.', 'The residue of the herbicide in the soil a year after application is not enough to control most weeds effectively.', 'The application of herbicides is less critical for soybean than for corn crops.']