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: Anatomy
Cavernous sinus thrombosis happens when infection reaches at 
Select and explain. 
A. Ethmoidal vein., B. Maxillary sinus, C. Pterygoid plexus of vein., D. Submental lymph nodes.
C: Pterygoid plexus of vein.
Answer: C: Pterygoid plexus of vein. 
Explanation: None