Dr. Jamshed wants to see if person’s IQ changes as they get older. To do this he takes three groups of subjects. Group i is made up of 10 years old, and Group III of 25 years old. Dr. Jamshed tests all three groups of their IQ level. The design of this experiment is called:

A. longitudinal study
B. more information is needed to determine the design of the experiment
C. Gesell’s dome
D. cross sectional study