D

Beveling (rounding) the pulpo-axial line angle removes the sharp internal corner, giving the amalgam more bulk and reducing stress concentration at that point; this helps avert internal cracking or bulk fracture of the amalgam restoration rather than protecting enamel or margins [Amorim et al., 1978, PMID 278834; Kinomoto et al., 2003, PMID 12797575].