A

Reasoning: Transseptal fibres are part of the gingival fibre group; they span from the cementum of one tooth to the cementum of the adjacent tooth across the interdental space and do not insert into alveolar bone. By contrast, horizontal, oblique and apical fibres are principal periodontal-ligament fibres that attach root cementum to the alveolar bone [Adams, 1979, PMID 105125; Becker, 1992, PMID 1510051].