Indifference Curves Drawn with Income and Leisure on the Axes

Indifference curves drawn with income and leisure on the axes are convex to the origin of the graph because

A) people are willing to give up income to obtain more leisure and vice versa.
B) the marginal hour of leisure time becomes less valuable as one works fewer hours and more valuable as one works more hours.
C) the marginal hour of leisure time becomes more valuable as one works fewer hours and less valuable as one works more hours.
D) utility increases as income and leisure increase.