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Birds and reptiles are both vertebrates that lay eggs but birds have beaks and reptiles have teeth. Occasionally birds have teeth but only in the embryonic stage. Which conclusion is best supported by the presence of teeth in bird embryos?

AAncestors of reptiles had beaks similar to those of birds.
BBirds and reptiles eat similar types of food.
CBirds and reptiles share a common ancestor.
DModern reptiles are the ancestors of modern birds.