Look at these two sets of pictures. When you change the coloring, you can change the feeling/mood of the picture. Pick a set of pics, and tell me
the mood each represents and why you think that.

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."

could you go a bit more in depth with you question? it's quite hard to understand. as soon as you do that i will be glad to : )