Lobbying is the term given to the activities of interest groups that seek to influence the making and inplementation of public policy and to persuade government officials to support a group position. these activities are directed at the

lobbyists direct their influencing at the legislators

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."