A nurse is providing teaching to the parent of an infant about introducing solid foods. The nurse should recommend that which of the following foods be introduced first?

A. Cooked egg whites should not be introduced to infants until later (around 1 year), as they can be a potential allergen and cause food sensitivities. B. Pureed meats are a good source of protein but are typically introduced after cereals. They can be an option after iron-fortified cereals. C. Strained fruits are usually introduced after iron-fortified cereal because they are not rich in iron, and iron is a priority at this developmental stage. D. Iron-fortified cereal is recommended as the first solid food because it provides a good source of iron, an essential nutrient for infants around 6 months old.