Austin Wants to Do His Honour's Thesis in Psychology in the Area

Austin wants to do his honour's thesis in psychology in the area of developmental psychology. He has eight months to decide on a specific topic, design the study, collect the data, analyze the results, and write the thesis. Assuming he is interested in comparing children's performance at different ages, what type of design would be the most practical for him to use?

A) sequential design.
B) double-blind design.
C) cross-sectional design.
D) longitudinal design.