Do we have total control over all the factors affecting physical fitness

it's false.

"every person has their limitations which prevent us from accomplishing something. some are better than mathematics for example and some are worse. those people who are worse might never be able to become mathematicians, but that does not mean that they would not be great at doing something else."

out of the choices i'd say d the ability to set goals, mainly because to desire to continue you need motivation but it isn't motivation in that part, but setting goals means you have an endgame and you want to reach it which sums up motivation.