Which of the following is true of the alternative minimum tax?

a. The alternative minimum tax is designed to ensure that high income taxpayers do not pay excessive amounts of income tax.

b. For 2015, the alternative minimum tax rates are 20 percent and 30 percent, depending on the taxpayer's income.

c. The amount of a taxpayer's state income tax may not be deducted for the purpose of computing the alternative minimum tax.

d. All tax-exempt interest is a tax preference item for the alternative minimum tax.

e. None of the above are true.