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
A test was considered for diagnosing a disease. Out of 80 positive cases with this test, 40 actually had no disease. Out of 9920 tested negative cases 9840 actually had no disease. Calculate the sensitivity of the test - 
Select and explain. 
A. 13%, B. 33%, C. 50%, D. 99%
B: 33%
Answer: B: 33% 
Explanation: Ans. is 'b' i.e., 33%