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
All except one are true regarding cavernous sinus 
Select and explain. 
A. Cavernous sinus roof is formed by meningeal layer of duramater, and floor is formed by endosteal layer of duramater., B. It is an unpaired venous sinus., C. 3rd and 4th cranial nerve and internal carotid artery pierce roof of cavernous sinus, D. Abducens nerve passes through the cavernous sinus.
B: It is an unpaired venous sinus.
Answer: B: It is an unpaired venous sinus. 
Explanation: Cavernous sinus is a paired venous sinus.