What has the World feared with Iran since 1979? A They would become the wealthiest Nation in the Middle East
B They would control the sale price of their valuable resource
C They would not allow women the right to vote
D They would obtain nuclear weapons

they would become the wealthiest nation in the middle east. that is the answer to your problem

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."