A TV commercial said that the prairie green bird chicken, who was hungry to eat grass and ate grasshoppers, seemed to imply that the nutritional value of the chicken and its eggs was related to the grassland food that the chicken ate. To verify this conclusion, which of the following experimental methods is the most reliable? ['Select a good breed of laying hens to feed on the grassland, and then compare with the nutritional composition of ordinary chickens fed on non-grassland.', 'Assay, comparing the nutritional content of chicken food on grassland and chicken food on non-grassland.', 'Select breeds and layers of exactly the same grade, half of which are fed on grasslands and half are fed on non-grasslands, and then compare their nutritional content.', 'Select different breeds of laying hens, feed them on the grassland, and compare their effective ingredients.']