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
. Which of the following is a characteristic of a point source epidemic ? 
Select and explain. 
A. Herd immunity regulates spread of cases, B. Person to person transmission is seen, C. Secondary wave of cases is always seen, D. All cases develop within one incubation period
D: All cases develop within one incubation period
Answer: D: All cases develop within one incubation period 
Explanation: None