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 type of sample can be used to isolate polio virus earliest 
Select and explain. 
A. Stool, B. Blood, C. Throat, D. CSF
A: Stool
Answer: A: Stool 
Explanation: None