<s>[INST] context: The child has the symptoms of primary carnitine deficiency. Carnitine cannot be transported from the blood into the liver and muscle, and fatty acid oxidation in those tissues is severely impaired. The inability to utilize fatty acids for energy gives rise to muscle weakness, and an accumulation of fatty acids can occur within the muscle tissue. The inability of the liver to oxidize fatty acids will lead to fasting hypoglycemia because there is insufficient energy for gluconeogenesis. An MCAD deficiency would not show fatty infiltration in the muscle, nor elevated levels of free fatty acids (the presence of medium- chain dicarboxylic acids, or acylglycines, would be observed instead). A defect in CAT II would result in acylearnitines in the circulation. An HMG-CoA synthase deficiency would not allow ketone body formation and would not present with these symptoms. A lack of acetyl-CoA carboxylase would greatly reduce the fatty acid content within the fat cell because endogenous fatty acids would not be able to be synthesized from acetyl-CoA. [/INST] question: A 4-month-old child exhibited extreme tiredness, irritable moods, poor appetite, and fasting hypoglycemia associated with vomiting and muscle weakness. Blood test showed elevated levels of free fatty acids, but low levels of acylcarnitine. A muscle biopsy demonstrated a significant level of fatty acid infiltration in the cytoplasm. The most likely molecular defect in this child is in which one of the following enzymes? | options: A: MCAD B: Carnitine transporter C: Acetyl-CoA carboxylase D: CAT II | answer: B </s>