And the reason we have two of these aldoses is because we have a single stereogenic carbon. We have a chiral carbon, and that means we're going to have two different isomers. These are known as enantomers. Enantomers are mirror images of one another. So we essentially, on this particular molecule, we don't have a mirror image because we don't actually have a stereogenic carbon. Remember, a stereogenic carbon is a carbon that is chiral, and that means it is attached to four different groups.