The main difference between appositional and interstitial growth is where it occurs and what happens when it occurs. For interstitial growth it occurs inside the bone going out that is why it is called interstitial meaning inside the tissue. What happens is the cartilage grows longer. When you talk about appositional, it occurs outside the bone, the periphery of cartilage. This happens on pre-existing cartilage making the cartilage thicker. With that, the answer to your question is B.
