Brady, who has ordinary-shaped indifference curves, buys 16 ounces of salt each year. Even when the price of salt doubles, Brady continues to purchase exactly 16 ounces. To help you answer this question, it may be helpful to use indifference curves and budget constraints to depict Brady's behavior graphically on a sheet of paper.

Which of the following statements is true?

a. Salt is an inferior good for Brady since the income effect is positive.
b. Salt is a normal good for Brady since the income effect is negative.
c. Salt is an inferior good for Brady since the income effect is positive.
d. Salt is a normal good for Brady since the income effect is positive.