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
Cyanide is toxic because it - 
Select and explain. 
A. Inhibits cytochrome oxidase, B. Forms cyan meth Hb, C. Inhibits ATP carrier in mitochondria, D. Inhibits Na-K-ATP ase
A: Inhibits cytochrome oxidase
Answer: A: Inhibits cytochrome oxidase 
Explanation: A i.e. Inhibits Cytochrome oxidase