In Developmental Research, Variables Are Assessed as a Function of Time

In developmental research, variables are assessed as a function of time. How does cross-sectional design work?

A) Groups divided by age are assessed at the same time.
B) One group is studied at different points over a long period of time.
C) Representative samples of different age groups are assessed multiple times over a long period.
D) It combines longitudinal and cross-sequential design.