Suppose we measure the quantity of good X on the horizontal axis and the quantity of good Y on the vertical axis If indifference curves are bowed inward, as we move from having an abundance of good X to having an abundance of good Y, the marginal rate of substitution of good Y for good X (the slope of the indifference curve) ?

• A. rises
• B. stays the same
• C. could rise or fall depending on the relative prices of the two goods.
• D. falls