What do you think are three most important developments leading up to America Civil War?

1) Industry rather than Farming

2) slavery

3) secession of the southern states

Explanation:

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."

its tr3way you already know