Which of the following is NOT an advantage of Egypt's geography? A. Natural desert barrier
B. Easily defensible mountains and hills
C. Rivers and waterways to trade
D. Regular river flooding

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."