Javaid is a graduate student who is studying the way in which selective attention develops during the preadolescent years. He selected a group of 10-years-olds, and he assesses their selective attention every six months over a two-year period. In this example, Javaid is using:

by

A. a longitudinal research design
B. a sequential design
C. a cross-sectional design
D. a multi-factorial research design