to represent the world, we must detect physical energy (stimulus) from the environment and convert it into neural signals, a process called sensations

the answer your looking for is c. : )

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; no longer than a reasonable period of time;

answer; /// the need to make choices because economic wants exceed economic means;