Which research design most directly tests how a major historical event changed public perceptions in a population over time?

• A. A cross-sectional snapshot conducted only after the event, with no baseline for comparison.
• B. A longitudinal study comparing survey responses on perceptions before and after the event, controlling for demographic change and media exposure.
• C. An ethnographic study of a single individual's life without reference to the wider population or pre-event attitudes.
• D. A laboratory experiment testing reaction times unrelated to perceptions or historical context.

Answer: (B)