Tucker is a graduate student who is studying identity formation. He selects a group of 5-year-olds, a group of 10-year-olds, and a group of 15-year old, and interviews each group, asking them what they plan to be when they finish school. In this example, Tucker is using

B). A Cross-sectional research design.

Explanation:

A cross-sectional research design is demonstrated as a kind of observation study that involves the study and analysis of a representative subset from the population at a particular point of time.

In the given example, Tucker is employing 'cross-sectional research design' as he selects a representative subset('a group of 5-year-olds, a group of 10-year-olds, and a group of 15-year old) from the population at the same time for study and analysis(by interviewing them) . This implies that Tucker adopts a 'cross-sectional research design.'

answer; fulfilling a goal of the president's council of physical fitness and sports;