In the Cross-Sectional Design

In the cross-sectional design,

A) groups of people differing in age are studied at the same point in time.
B) participants are studied repeatedly at different ages, and changes are noted as they get older.
C) participants are presented with a novel task, and researchers follow their mastery over a series of closely spaced sessions.
D) the investigator conducts several sequences and makes cross-sectional comparisons.