Critical Reasoning

A 1991 calculation was made to determine what, if any, additional health-care costs beyond the ordinary are borne by society at large for people who live a sedentary life. The figure reached was a lifetime average of $1,650. Thus people's voluntary choice not to exercise places a significant burden on society.
Which one of the following, if true and not taken into account by the calculation, most seriously weakens the argument?

(A) Many people whose employment requires physical exertion do not choose to engage in regular physical exercise when they are not at work.

(B) Exercise is a topic that is often omitted from discussion between doctor and patient during a patient's visit.

(C) Physical conditions that eventually require medical or nursing-home care often first predispose a person to adopt a sedentary lifestyle.

(D) Individuals vary widely in the amount and kind of exercise they choose, when they do exercise regularly.

(E) A regular program of moderate exercise tends to increase circulation, induce a feeling of well-being and energy, and decrease excess weight.

The OA is C.

Experts, I want your explanations here. Please.