According to james marcia, the status of individuals who have made a commitment but not experienced a crisis is

The status of individuals who have committed but not experienced a crisis is a term of james Marcia which is called the identity status. The identity statuses are composed of four which are called the foreclosure, identity diffusion, moratorium and identity achievement. They deal with the commitment and crisis of one person exhibits.

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."