The libertarian party is an example of a party that is centered on

It is the only political association which regards you as a one of a kind and capable individual. The slogan is that we are "The Party of Principle", since we stand solidly on our standards. Libertarians unequivocally contradict any administration impedance into their own, family, and business choices.

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."