Most American children eat potatoes every day, but they don't know which part of potato is most nourishing .Take a sharp knife and cut a very thin slice  from it and hold it to the light, and you will see that the potato has skin, an outside rim  and the inner part. The outside rim which is right under the skin is most nutritious.But this part is often thrown away with the skin. Even the skin itself is better for food than the inside. When eating a cooked potato, if you choose the inside and leave the outside, you are wasting the best part of it. If you can't eat the whole potato, it is better to eat the outside rim and leave the inner part. A potato has   _  .
one part only two parts three parts four parts