Single best answer: A  

Reasoning: The maxillary (upper) lateral incisor has comparatively pronounced marginal ridges and often a linguo-gingival (palatogingival) groove, giving it a deeper, more sharply defined lingual fossa than the maxillary central or any mandibular incisors. Clinical and anatomic studies note that lingual developmental grooves and pits—features that accompany a deep lingual fossa—occur predominantly on maxillary lateral incisors, not on centrals or mandibular incisors [Pécora et al., 1991, PMID 1819358].