Pluto the dog is hit by a car while chasing a squirrel. afterward, he starts losing weight and does not seem interested in eating his food. pluto is most likely having problems with the part of the brain that processes the hormone which should indicate when to stop eating.

The correct answer is the leptin. The leptin is known as the hormone responsible for energy expenditure. This is the hormone that helps an individual to regulate the energy balance by having to be able to inhibit hunger and that it is opposed by actions of the hormone called ghrelin which is known as the hungry hormone.

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."