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: Medicine
21 year old female presents with history of mild bilateral ptosis, proximal muscle weakness and easy fatiguability which among the following is best in diagnosing this condition - 
Select and explain. 
A. Muscle biopsy, B. Edrophonium test, C. Repetitive nerve stimulation, D. Electro myography
B: Edrophonium test
Answer: B: Edrophonium test 
Explanation: None