21.Which of the following correctly describes a key regulatory mechanism of lipid Boxidation? (A) Malonyl-CoA inhibits carnitine acyltransferase I (CPT I), preventing long-chain fatty acids from entering the mitochondrial matrix. (B) Insulin directly activates β-oxidation by increasing CPT I activity and promoting mitochondrial fatty acid import. (C) Elevated NADH levels enhance the activity of β-hydroxyacyl-CoA dehydrogenase, accelerating B-oxidation. (D) Fatty acid β-oxidation occurs primarily in the cytosol rather than in mitochondria. (E) Activation of AMP-activated protein kinase (AMPK) suppressesβ-oxidation by inhibiting fatty acid transport into mitochondria.