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
Tricarboxylic acid cycle to be continuous requires the regeneration of 
Select and explain. 
A. Pyruvic acid, B. oxaloacetic acid, C. α-oxoglutaric acid, D. Malic acid
B: oxaloacetic acid
Answer: B: oxaloacetic acid 
Explanation: Oxaloacetate may be viewed as a catalyst, which enters into the reaction, causes complete oxidation of acetyl CoA and comes out of it without any change.
Reference: Vasudevan 7th  ed, pg 249