The answer is a) sagittal suture.
The sagittal suture is the fibrous joint that runs along the top of the skull, separating the left and right parietal bones. It articulates with a total of five bones: the frontal bone at the anterior aspect, the two parietal bones, and the occipital bone at the posterior end. In comparison, the squamosal suture articulates with the temporal bones, the lambdoid suture connects the parietal bones and the occipital bone, and the coronal suture joins the frontal bone with the two parietal bones. Thus, the sagittal suture has the distinction of connecting the greatest number of cranial bones.