Giselle became an AMT taxpayer last year. As a result, she had to add several items to her taxable income in arriving at alternative minimum taxable income. Which of the following items will result in an AMT credit that can be used to offset future regular tax liability?

a. $5,000 in property taxes paid on her principal residence.

b. $75,000 difference between the fair market value of stock and the strike price in the incentive stock option used to purchase the stock.

c.$4,000 in interest on private activity municipal bonds.

d.$4,000 in additional medical expenses.