This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Urea Cycle and Disorders, Subject name: Biochemistry
Urea cycle linked to kreb's cycle by? 
Select and explain. 
A. Fumarate, B. Oxaloacetate, C. Ornithine, D. Citrullin
A: Fumarate
Answer: A: Fumarate 
Explanation: ANSWER: (A) FumarateREF: Harper's illustrated biochemistry 27th ed p. 246-49Arginosuccinate is converted to arginine at this step fumarate is released. At this step urea cycle cycle is linked with TCA cycle.