###Rationale: (a) Cerebrospinal fluid is formed by vascular choroid plexus in the ventricles in the brain; the letter "A" indicates the lateral ventricle.

###Answer: OPTION A IS CORRECT.
###Question: 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?
###Options:
A. A
B. B
C. C
D. D
