Would Be the Very Best Research Design to Determine Whether

would be the very best research design to determine whether middle-aged adults are really more psychologically "mature" than young adults?

A) a longitudinal design, with a large representative sample studied from 20 to 45
B) a cross-sectional study in which a large, representative sample of adults of each age from 20 to 45 (e.g., 20-year-olds, 25-year-olds, etc.) is studied once
C) the same cross-sectional design as in b, but repeated at 10-year intervals
D) a sequential design in which each age interval is studied longitudinally in more than one cohort