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
"Lead time" is, 
Select and explain. 
A. Time between disease onset and first possible point of diagnosis, B. Time between first possible point of diagnosis and usual time of diagnosis, C. Time between disease onset and final critical diagnosis, D. Time between disease onset and usual time of diagnosis
B: Time between first possible point of diagnosis and usual time of diagnosis
Answer: B: Time between first possible point of diagnosis and usual time of diagnosis 
Explanation: None