Eron and Colleagues Conducted a Longitudinal Study into the Relation

Eron and colleagues conducted a longitudinal study into the relation between TV viewing and aggression. What does the term "longitudinal" mean?

A) The design had a "Latin Square" configuration, which included longitude as well as latitude
B) Participants were tested over several days
C) Participants were recruited from different geographical regions, but all of the same longitude
D) Many different age groups were tested
E) Participants were tested at several points in time over a long period, in this case several decades