Indifference Curves Are Convex to the Origin Because

Indifference curves are convex to the origin because:

A) at a lower income,a person is more willing to sacrifice income for additional leisure
B) at a lower income,a person is less willing to sacrifice income for additional leisure
C) at any income level,a person is willing to sacrifice the same amount of income for additional leisure
D) the marginal rate of substitution of leisure for income is negative