Why Don't Most Tax Expenditures Help Much If Your Federal

Why don't most tax expenditures help much if your federal tax bill is zero?

A) Taxes are an automatic stabilizer.
B) Most tax expenditures are specifically for high-income people.
C) You don't qualify for tax breaks if your federal tax bill is zero.
D) Most tax breaks reduce taxable income, but reducing taxable income below zero does not reduce the tax bill.