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: Unknown
In epidemic, 1st step is? 
Select and explain. 
A. Verification of diagnosis, B. Isolation, C. Immunization, D. Notification
A: Verification of diagnosis
Answer: A: Verification of diagnosis 
Explanation: The steps in epidemic investigation are :

Verification of diagnosis
Confirmation of the existence of epidemic
Defining the population at risk
Obtaining a map of the area
Counting the population
Rapid search for all cases & their characteristics
Medical survey
Epidemiological case sheet
Searching for more cases
Data analysis
Formulation of hypothesis
Evaluation of ecological factors
Further investigation of population at risk
Writing the report