This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Pharmacodynamics, Subject name: Pharmacology
X in the graph represents 
Select and explain. 
A. Therapeutic index, B. Therapeutic dose, C. Therapeutic window, D. Therapeutic efficacy
C: Therapeutic window
Answer: C: Therapeutic window 
Explanation: Therapeutic index : LD50/ED50 Therapeutic window Range of steady-state concentrations of drug that provides therapeutic efficacy with minimal toxicity Therapeutic efficacy: Ability of a drug to activate a receptor and generate a clinical response is Therapeutic efficacy Therapeutic dose: Dose of a drug required to have a clinical response