The idea that it was the
right of Americans to
expand westward to the
Pacific Ocean

Mark me as brain list and here you go your answer is in the picture

i believe that the answer to the question provided above is that the role of campaign committees is to act as a bridge between state and local campaigns.

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."