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: Surgery
Guerin's sign is: 
Select and explain. 
A. Ecchymosis at greater palatine foramen, B. Ecchymosis at mastoid foramen, C. Ecchymosis at condylar region, D. Ecchymosis at infraorbital foramen
A: Ecchymosis at greater palatine foramen
Answer: A: Ecchymosis at greater palatine foramen 
Explanation: None