Why Is the Threat of Participant Attrition More Problematic in Longitudinal

Why is the threat of participant attrition more problematic in longitudinal designs than in other types of descriptive research?

A) Participants are elderly.
B) Data analysis is complex, and missing data points necessitate dropping the participant from the analysis.
C) Data collection occurs over a much longer period of time.
D) Treatments are aversive, making participants in the experimental group drop out.