Jill wants to get more active, but is having trouble motivating herself to engage in more physical activities. she talks with a friend and they decide to motivate each other to be more active by documenting the number of physical activities they engage in each week. if they meet a certain requirement, they reward themselves with a gift or a leisure activity. which approach are jill and her friend using to motivate themselves?

The approach that Jill and her friend is doing the motivation and reward system.  In this system, a set of goal is being targeted and a reward is being accomplished after reaching the goal. In this case, Jill and her friend reward themselves by getting a gift or doing a leisure activity.

d. i assume the underlined word is "role." reformat if it isn't.

explanation:

role is closest to part because when replacing words, "playing a vital decision," "playing a vital activity," and "playing a vital dollar" don't make logical sense. the only meaningful choice is "playing a vital part."

this fits one of merriam-webster's definitions of role: "a function or part performed especially in a particular operation or process."