If the movie workers wanted to slowly lower the car to the cliff's bottom, they might hook the car to a a system of wheels and ropes.

i think this would be a pulley system.

its d i know cause i've been googling it

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."