The idea that there is a curvilinear relationship between happiness and task performance is readily explained by .

the consumer demand because the members have to be aware if people are going to buy what they want to sell in this case either energy drinks or a car wash.

is there multiple choice or do you need like an essay answer?

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."