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
The electron flow in cytochrome C oxidase can be blocked by 
Select and explain. 
A. Rotenone, B. Antimycin-A, C. Cyanide, D. Actinomycin
C: Cyanide
Answer: C: Cyanide 
Explanation: Inhibitors of Electron transport chain (Respiratory chain)

Complex I :- Barbiturates (amobarbital), piercidin A, rotenone, chlorpromazine, guanithidine.
Complex II Carboxin, TTFA, malonate.
Complex HI Dimercaprol, BAL, actinomycin A, Naphthyloquinone.
Complex IV (cytochrome c oxidase) :- Carbon monoxide (CO), cyanide (CN),H2S, azide (N3-)