As the large butterfly flew toward Richard, he could tell it was getting closer because he could feel his eyes turning inward toward his nose as he watched it. In this instance, Richard was able to judge how far away the butterfly was using the depth cue of

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."

answer; genetics;