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
ED 50 is a measure of: 
Select and explain. 
A. Toxicity, B. Safety, C. Potency, D. Efficacy
C: Potency
Answer: C: Potency 
Explanation: Potency can be defined as the concentration of drug EC50 or dose ED50 of a drug required to produce fifty percent of that drug's maximum Therapeutic effect. Ref: KDT, 6th Edition, Pages 53, 54; Basic and Clinical Pharmacology By Beram Katzung, 10th Edition, Page 28; Pahrmacology By Gary. C. Rosenfeld, David S. Loose, 4th Edition, Page 5