Which of the following is considered to be part of the biosphere? A) a cloud in the sky
B) a tree in the forest
C) a rock on the side of a mountain
D) a grain of sand on the beach

cord : Jaydennn # 2986

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; limbic system;

answer; provide for the common defense: