This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Head & Neck, Subject name: Anatomy
Choose the appropriate lettered structure in this radiograph of the lateral view of the head. Cerebrospinal fluid is formed by vascular choroid plexus in which structure? 
Select and explain. 
A. A, B. B, C. C, D. D
A: A
Answer: A: A 
Explanation: (a) Cerebrospinal fluid is formed by vascular choroid plexus in the ventricles in the brain; the letter "A" indicates the lateral ventricle.