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: Social & Preventive Medicine
When a drug is evaluated for its usefulness in controlled conditions, it is termed as a trial signifying - 
Select and explain. 
A. Efficacy, B. Effectiveness, C. Efficiency, D. Effect modification
A: Efficacy
Answer: A: Efficacy 
Explanation: None