This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory chain, Subject name: Biochemistry
CO acts by inhibiting which component of respiratory chain 
Select and explain. 
A. Cytochrome B, B. Cytochrome C oxidase, C. NADH CoQ reductase, D. Oxidative phosphorylation
B: Cytochrome C oxidase
Answer: B: Cytochrome C oxidase 
Explanation: Carbon monoxide is toxic for mitochondria in man, altering the mitochondrial respiratory chain at the cytochrome c oxidase level. This inhibition in cytochrome c oxidase may play a role in the development of the symptoms observed in acute CO poisoning, and in some diseases related to smoking