This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
All of the following molecules, without fuher metabolism, can cross the inner membrane of functioning mitochondria, EXCEPT: 
Select and explain. 
A. ATP, B. Acetyl CoA, C. Inorganic phosphate, D. Pyruvate
B: Acetyl CoA
Answer: B: Acetyl CoA 
Explanation: The size and the charge on CoA derivatives prevents their transpo. Thus the cell has two pools of CoA derivatives, cytoplasmic and mitochondrial.