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: Microbiology
Diphtheria toxin acts by - 
Select and explain. 
A. Inhibiting acetyl choline release, B. Inhibiting glucose transport, C. Increasing levels of cyclic AMP, D. Inhibiting protein systhesis
D: Inhibiting protein systhesis
Answer: D: Inhibiting protein systhesis 
Explanation: None