Aformal organization of people that seeks to influence government actions and policies by electing its members to public office.

a) political party
b) interest group
c) convention
d) political action committee

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."

answer; being clearly political;

answer; explanatory study;