Suppose the marginal costs of exercising are constant and the marginal benefits of exercising decline over time. With marginal costs and benefits placed on the vertical axis and time placed on the horizontal axis, the resulting marginal cost curve would be a line and the resulting marginal benefit curve would be .

horizontal, downward-sloping

Explanation:When marginal costs of exercising are constant and the marginal benefits of exercising decline over time. Plotting a graph With marginal costs and benefits placed on the vertical axis and time placed on the horizontal axis, the resulting marginal cost curve would be a horinzintal line and the resulting marginal benefit curve would be a downward slope.

answer; ///i believe that the correct answer is (a) it is the means by which a person earns money;