Which of the following is considered a peripheral?

On February 28, 2003, President George W. Bush issued Homeland Security Presidential Directive 5, which created ____________________________

Fill in the blank(s) with correct word

This type of study occurs over long periods of time and the same group of subjects is followed over extended periods at multiple times throughout the study period:

A) ?Retrospective study B) ?Prospective study C) ?Cross-sectional study D) ?Longitudinal study