This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Pharmacology
True regarding the following is 
Select and explain. 
A. A is having highest efficacy, B. A is having least potency, C. D is having highest potency, D. C is least potent
D: C is least potent
Answer: D: C is least potent 
Explanation: The picture shows dose response curves of various drugs in which right sided is most potent (least dose is required to produce effect), left is least potent(high dose required to produce the effect). So drug C is least potent. Efficacy is estimated by height -Drug D is most efficaciousRef: Katzung 11th ed pg 31