Which type of egg must be virtually clean according to grading standards?

In the context of egg grading standards, A-grade eggs must meet specific quality criteria, including having a virtually clean surface. This is important because cleanliness is a key aspect of egg appearance and quality perception. A-grade eggs are typically sold to consumers and are expected to show no blemishes or stains on their shells, as this reflects their freshness and overall quality.

B-grade and C-grade eggs, on the other hand, are generally of lower quality. B-grade eggs can have some slight stains or minor imperfections, while C-grade eggs are often used in processing or for baking and may have more extensive blemishes or other imperfections. As for organic eggs, they follow specific regulations pertaining to organic farming, but cleanliness at grading refers primarily to the surface condition, not the organic certification itself.

Thus, the correct answer regarding which type of egg must be virtually clean according to grading standards refers specifically to A-grade eggs, as they represent the highest quality expected in the market.