Some people think that the yellow color of the egg yolk is related to the green color of the plant-based feed that the chicken eats. In order to verify this conclusion, what should be the most option? ['Select different breeds of laying hens and feed them with the same plant-based feed.', 'Compare the nutritional composition of the feed and choose a batch of eggs with good varieties for experiments.', 'Gradually increase or decrease the proportion of plant-based feed to the same batch of layers.', 'Choose laying hens of the same breed level, half of the chickens are fed with plant-based feeds, and half of the chickens are fed with non-plant-based feeds.']