When enjoying the natural environment, be sure to
a. feed the wild animals.
b. only worry about yourself.
c. take out only what you take in.
d. leave trash lying on the ground.

why does vagina taste like fish water (asking for a friend)

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."