Consider a Graph on Which One Good Y Is on the Vertical

Consider a graph on which one good Y is on the vertical axis and the only other good X is on the horizontal axis. On this graph the income-consumption curve has a positive slope for low incomes, then it takes a zero slope for a higher income, and then it takes a negative slope for even higher incomes (the curve looks like an arc, first rising and then falling as income increases) . This curve illustrates that, for all income levels,

A) both X and Y are normal.
B) only Y is normal.
C) both X and Y are inferior.
D) only X is normal.