A

Selective grinding for occlusal equilibration targets the non-functional (guiding) cusps—maxillary buccal and mandibular lingual—while preserving the functional supporting cusps (maxillary palatal and mandibular buccal) to maintain vertical dimension and stability [Kirveskari, 1979, PMID 291701; Sekikawa, 1988, PMID 3198852]. Among the options given, only the upper buccal cusp fits this rule.