This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Link reaction, Subject name: Biochemistry
[{'content': 'All of the following are tightly bound to component enzymes of pyruvate dehydrogenase, EXCEPT \nSelect and explain. \nA. Thiamine pyrophosphate, B. Lipoic acid, C. Flavin adenine dinucleotide, D. Coenzyme A', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]