Read the following sentences: "When muscles work, they somehow communicate with the brain, liver an other organs. Until recently, scientists weren't sure how muscles sent those messages."
As used in the passage, communicate means
o be in touch with
to trade cells
use IL-6
to fight with

People who utilizes the progression principle will ensure their exercise program increases in frequency, intensity, time, and type. the changes need to happen gradually in order to ensure they make gains in their fitness program. a person who doesn't utilize the progression principle can still gain health benefits from exercising, but will not continue to improve in cardiovascular fitness.

Well i guess u know a lot of that, huh? that's nasty of me, isn't it? lol

Ibelieve the answer is b,hope my answer has you : )

Ansindividual insurance;