Question

adhering to the surface of the brain is the
dura mater.
psf
pia mater.
csf.

Explanation:

The pia mater is the innermost of the three meninges (membranes) that cover the brain and spinal cord. It adheres closely to the surface of the brain, following its contours and sulci. The dura mater is the tough outer - most layer, PSF is not a relevant meningeal structure in this context, and CSF (cerebrospinal fluid) surrounds the brain but does not adhere to its surface.

Answer:

pia mater.