Which is not an option under consideration for the future of Puerto Rico? A. remain a Commonwealth
B. become a U. S. state
C. become a Cuban territory
D. become an independent country

  b.

there are isolated pockets of farming, generally around rivers and oases, which are used for irrigation.

it is a better alternative

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."