Now, these are epimers, because they only differ in their stereo chemistry at a single one of these chiral carbon atoms. And let's see which one that is. So, if we begin at the first carbon, the first chiral carbon, notice that the hydroxyl group points to the right and the hydroxyl group here points to the right as well. Now, if we move on to the second stereogenic hydrocarbon, we'll see that the hydroxyl actually points to the left in D glucose, but it points to the right. And D mannose. If we move on to the third stereogenic carbon, we'll see that once again, they point to the same side.