B

Reasoning: On a Stephan pH curve, the greatest demineralization—and therefore highest caries risk—occurs at the nadir reached a few minutes after sugar intake, when plaque pH is well below the critical value of 5.5. This lowest point is conventionally labelled Point B, so caries is most likely to develop there (Bowen 2013, PMID 23224410; Fejerskov 1992, PMID 1740552).