In determining a corporation's taxable income for state income tax purposes, which of the following does not constitute a subtraction modification from Federal income?

a. Expenses that are directly or indirectly related to state and municipal interest that is taxable for state purposes.

b. The amount by which the Federal depreciation deduction exceeds the corresponding state amount.

c. The amount by which the state depreciation deduction exceeds the corresponding Federal amount.

d. Interest on U.S. obligations.