D

Reasoning: Odontoblasts form a true single layer that lines the entire pulp chamber; however, the tall columnar cells crowd together so that their nuclei lie at different heights, giving the layer a pseudostratified, palisading appearance and making it look 3–5 cells thick in routine sections [Lyn et al., 1991, PMID 1820812; Ohshima & Yoshida, 1992, PMID 1499052].