Why is it the matrix? Well, because in stage three, within the matrix, those fatty acids are actually broken down into acetyl coenzyme A molecules. And then these acetyl coenzyme A molecules are fed into the citric acid cycle and that helps the cell generate ATP molecules. So what I'd like to focus on in this lecture is stage two. So the activation of the fatty acids and the subsequent transport into the matrix of the mitochondria. So, as we go through the following text, let's use this diagram as our reference.