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: Pathology
The least common site for a berry aneurysm is - 
Select and explain. 
A. Vertebral artery, B. Basilar artery, C. Junction of anterior cerebral artery and internal carotid artery, D. Posterior cerebral artery
A: Vertebral artery
Answer: A: Vertebral artery 
Explanation: A berry aneurysm

The further away the aneurysm from the anterior circulation or from the circle of willis , the less common will be its rate of occurance.
Berry an aneurysm or Saccular aneurysm or Congenital aneurysm is the most frequent type of intracranial aneurysm.
Most aneurysms occur in the anterior circulation and are found near the branch points.
The most common site is junction between anterior cerebral artery and anterior communication artery (40%).
Next most common site is internal carotid artery and posterior communicating artery (20%)

Less frequent sites include -

Top of basilar artery
Junction of basilar artery and the superior cerebllar artery or anterior inferior cerebellar artery.
Junction of vertebral artery and posterior inferior cerebellar artery.