Answer: D

Reasoning: Dummer and co-workers classified the shape of the root-canal terminus into four types—Type 1 (traditional single constriction), Type 2 (tapering/funnel-shaped), Type 3 (parallel canal walls) and Type 4 (multiple or “multi-constricted” narrowings near the apex). Because the question asks for the category with several successive constrictions, it corresponds to Type 4 of this classification [Dummer PMH et al., 1984; Chang JW et al., 2022, PMID 35692230].