Often, an antagonistic relationship called a drives the plot of a story or novel.

conflict

Explanation:

A conflict will drive a story , as a struggle between two opposing forces or characters with different interests in a fictional setting. The conflict will make up the guiding line for the story to unfold.

The narrations always include some way of conflict , the characters engage in interactions and overcome obstacles or face situations where drama and other elements like suspense , thriller come along in a story.

Usually a conflict arises in the middle or climax and has a beginning , development and a end, this will make events and actions take a course and lead to a story to unveil.

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."