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: Pharmacology
Drug which is useful for the diagnosis of myasthenia gravis is? 
Select and explain. 
A. Neostigmine, B. Physostigmine, C. Edrophonium, D. Atropine
C: Edrophonium
Answer: C: Edrophonium 
Explanation: The two types of weakness require opposite treatments. They can be differentiated by edrophonium test.