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
The number of patients required in a clinical trial to treat a specify disease increases as 
Select and explain. 
A. The drop-out rate increases, B. The significance level increases, C. The size of the expected treatment effect increased, D. The incidence of the disease decreases
A: The drop-out rate increases
Answer: A: The drop-out rate increases 
Explanation: None